seismic imaging of subduction zone metamorphism combined analysis of high resolution seismic images of the alaska and cascadia subduction zones reveals where metamorphic fl uids are released both images show the subducted oceanic crust as a dipping low velocity layer with a clear termination depth however in alaska the crust is thicker 15 20 km compared to 8 km and terminates at greater depth 120 km com pared to 40 km than in cascadia based on metamorphic reaction estimates and geodynamic models we demonstrate that the termination depth corresponds to eclogitization of the crust triggered by dehydration of water bearing minerals and that the location of this reaction is dependent on the thermal structure of the subducted slab

western hellenic subduction and cephalonia transform local earthquakes and plate transport and strain abstract focal parameters of local earthquakes in the region of the ionian islands of western greece are constrained with a temporary dense array of three component seismographs operated jointly offshore and onshore seismic deformation is documented to be confined to the east of the n20 e striking steep continental slope west of cephalonia island the right lateral cephalonia transform fault ctf inferred from large earthquakes the pre apulian continental material appears to be only deforming east of the transform fault where it is in upper plate position to the hellenic subduction east of the transform fault the transmission velocity tomography from local earthquakes compared in depth section with a previous marine reflection profile provides evidence in support of a shallow landward dipping boundary around 12 km deep under the ionian islands along which they may override the lower plate on either side of this interface local earthquakes occur with different focal mechanisms in support with its interpretation as the interplate under cephalonia island reverse faulting deforms the upper plate along nw se structures which may also be affected by left lateral bookshelf faulting small earthquakes show normal faulting along the western coast of cephalonia and its extension 20 km ssw the trace of the ctf as inferred from the occurrence of the large strike slip earthquakes another group of normal fault earthquakes locates in the lower plate from under cephalonia to zante just outboard of a possible change of interplate dip suggested from reflection seismics landward under the islands these normal fault earthquakes appear to coincide in position with that of the load imposed by the upper plate transported over them rather than occurring in an outer rise outboard the plate boundary and trench as observed in other subductions and attributed to the control by the flexural bending of the lower plate under the pull of the sinking slab interpretation has to consider several peculiar features of plate interaction in western greece with respect to a steady state model for major subduction zones in particular a fast deformation of the upper plate in front of an orogenically overthickened crust and of the southwestward push of extruding anatolia its transport which is the cause of the migration of the plate boundary rather than the roll back of a slab which has been proposed to be detached possibly a flat and ramp shape of the interplate the geometrical complexity of the shear limit across the ctf between subduction and collision and the nearby variation of the nature of the foreland crust

salman farsi dam reservoir a successful project on a karstified foundation sw iran the salman farsi dam is constructed on the ghareh aghaj river at the northern limb of changal anticline sw iran the anticline is composed of the calcareous asmari formation af sandwiched between two marly formations the pabdeh gurpi pgf and razak rf the af is divided into three units lower laf marl and limestone middle maf karstified limestone and upper uaf marl and marly limestone the dam is constructed on the maf and the reservoir is in direct contact with the maf uaf and rf a huge relict cave was discovered during excavation of grouting galleries in the maf in this research the potential leakage passage plp is defined as parts of the karst aquifer located lower than the normal water level nwl of reservoir in which the reservoir water has potential to be leaked toward downstream assuming no grout curtain construction the plp is composed of the inlet windows transfer passage and discharge zones at the salman farsi dam the plp is determined by three alternative schematic models considering hydrogeological and geological settings at this dam site the grout curtain was properly designed from the maf toward the downstream laf at the narrowest part of the plp and bypassing the huge cave the grout curtain was successful in blocking the plp based on the negligible leakage and high differences between water level in the pair piezometers at the upstream and downstream sides of the grout curtain it is recommended to determine the plp in future dam construction in karst terrains

new constraints on the active tectonic deformation of the aegean 1 site velocities from six separate global positioning system gps networks comprising 374 stations have been referred to a single common eurasia fixed reference frame to map the velocity distribution over the entire aegean we use the gps velocity field to identify deforming regions rigid elements and potential microplate boundaries and build upon previous work by others to initially specify rigid elements in central greece the south aegean anatolia and the sea of marmara we apply an iterative approach tentatively defining microplate boundaries determining best fit rigid rotations examining misfit patterns and revising the boundaries to achieve a better match between model and data short term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long term kinematics we find that present day aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them the rms misfit of model to data is about 2 sigma very good when compared to the typical match between coseismic fault models and gps data the simplicity of the microplate description of the deformation and its good fit to the gps data are surprising and were not anticipated by previous work which had suggested either many rigid elements or broad deforming zones that comprise much of the aegean region the isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain year nstrain year 10 9 year 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries lower strain rates may exist elsewhere within the microplates but are only resolved in anatolia where extension of 13 4 nstrain year is required by the data our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity active faulting fault geomorphology and earthquake fault plane solutions continental tectonics at least in the aegean is to first order very similar to global plate tectonics and obeys the same simple kinematic rules although the widespread distribution of aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized

seismic investigation of the transition from continental to oceanic subduction along the western hellenic subduction zone 1 the western hellenic subduction zone whsz exhibits well documented along strike variations in lithosphere density i e oceanic versus continental subduction rates and overriding plate extension differences in slab density are believed to drive deformation rates along the whsz however this hypothesis has been difficult to test given the limited seismic constraints on the structure of the whsz particularly beneath northern greece here we present high resolution seismic images across northern and southern greece to constrain the slab composition and mantle wedge geometry along the whsz data from two temporary arrays deployed across greece in a northern line nl and southern line sl are processed using a 2d teleseismic migration algorithm based on the generalized radon transform images of p and s wave velocity perturbations reveal n60e dipping low velocity layers beneath both nl and sl the 8 km thick layer beneath sl is interpreted as subducted oceanic crust while the 20 km thick layer beneath nl is interpreted as subducted continental crust the thickness of subducted continental crust inferred within the upper mantle suggests that 10 km of continental crust has accreted to the overriding plate the relative position of the two subducted crusts implies 70 85 km of additional slab retreat in the south relative to the north overall our seismic images are consistent with the hypothesis that faster sinking of the denser oceanic portion of the slab relative to the continental portion can explain the different rates of slab retreat and deformation in the overriding plate along the whsz

variation of seismic coupling with slab detachment and upper plate structure along the western hellenic subduction zone abstract the western hellenic subduction zone is characterized by a trenchward velocity of the upper plate in the ionian islands segment complete seismic coupling is achieved as is predicted by standard plate tectonic models in which there is no slab pull force because the slab has broken off the moderate local seismic moment rate relates to a shallow downdip limit for the seismogenic interface this characteristic may be attributed to the ductility of the lower crust of the upper plate which allows a decollement between the upper crust of the overriding plate and the subducting plate farther south a deeper downdip limit of the seismogenic interface is indicated by thrust faulting earthquakes which persist much deeper in western crete a correspondingly larger downdip width of this seismogenic zone is consistent with the suggested larger maximum magnitude of earthquakes here however since the seismic moment release rate seems to be moderate in the peloponnese and western crete like in in the ionian islands this seismically active interface cannot maintain complete seismic coupling across its larger downdip width a cause may be the lateral addition of overweight to the part of the slab still attached in crete by the free fall of its part that has broken off from the surface further north this increased slab pull reduces the compressive normal stress across the seismogenic interface and thus causes partial seismic coupling in its shallower part however the width of this part may provide an additional area contributing to slip in large earthquakes which may nucleate deeper on stick slip parts of the interface hints at anomalies in structure and seismicity which need to be resolved may relate to the present location of the edge of the tear in the slab

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

the oceanic nature of the african slab subducted under peloponnesus thin layer resolution from multiscale analysis of teleseismic p to s converted waves summary in the hellenic subduction zone the lithospheric slab may comprise continental and oceanic units juxtaposed downdip and along strike for stations along eastern peloponnesus teleseismic p wave receiver function rf processing in the standard frequency band produces an image of a low velocity layer lvl at the top of the slab apparently twice thicker than for an oceanic crust to assess if this could come from a lack of resolution of the standard processing we develop a multiscale approach with the rfs based on the wavelet response of the medium akin to the wavelet transform of the velocity depth function the synthetic response in conversion is obtained for a multiscale singularity formed by two opposite velocity steps at the boundaries of a crust embedded in mantle material this indicates that only wavelet periods shorter than about 0 8 s will allow to identify clearly a 7 km thin oceanic crust going to longer periods leads to underestimate or overestimate the time thickness of the lvl due to interference phenomena the analysis of the response in conversion from full waveform synthetic seismograms in a dipping slab model validates a multiresolution approach to real observations with earthquakes of broad enough spectrum towards high frequencies yielding energy to provide wavelet periods significantly shorter than 1 s the p to s conversions obtained allow us to resolve for the first time a standard oceanic crust at the slab top beneath the eastern coast of peloponnesus this documents the subduction of a purely oceanic slab of most reduced buoyancy since 4 5 myr under the rapidly southwestward extending upper plate continental material

late cenozoic deformation of the hellenide foreland western greece the late cenozoic structural evolution of western greece involved the shortening of mesozoic passive continental margin and cenozoic foreland basin sequences in a foreland propagating fold and thrust system and superimposed neotectonic deformation related to the development of an active island arc although the pre apulian zone has been regarded as the undeformed western foreland to the thrust belt three dimensional exposures in the ionian islands of kephalonia and zakinthos afford evidence of significant late neogene and quaternary shortening including thrusting on reactivated normal faults time relations and fault kinematics show that these structures are compatible with the westward migration of the locus of hellenide thrusting beyond its previously recognized limit and outer arc compression related to active subduction the presence of the pre apulian zone in the west contrasts with other aegean foreland areas where no such intermediate block lay between the thrust pile and old mesozoic oceanic crust consequently the pre apulian block took up continued hellenide shortening in the late miocene while oceanic crust was being overridden subducted in southern parts of the arc to the east the pre apulian zone subsequently overrode the ocean floored ionian sea during the late neogene the confusion in determining driving mechanisms for late cenozoic deformation in western greece and the apparent conflict between evidence for the age of initial subduction in different parts of the arc are explained by this model which is consistent with regional considerations including structuration in adjacent areas and important paleomagnetic rotations in the arc

slab segmentation controls the interplate slip motion in the sw hellenic subduction new insight from the 2008 mw 6 8 methoni interplate earthquake we present an integrated approach of the seismic structure and activity along the offshore sw hellenic subduction from combined observations of marine and land seismic stations our imaging of the slab top topography from teleseismic receiver function analysis at ocean bottom seismometers supports a trenchward continuation of the along dip slab faults beneath the peloponnesus we further show that their morphostructural control accounts for the backstepping of the thrust contact of the mediterranean ridge accretionary wedge over the upper plate local seismic activity offshore sw peloponnesus constrained by ocean bottom seismometer observations reveals a correlation with specific features of the forearc the matapan troughs we study the mw6 8 14 02 2008 interplate earthquake offshore sw peloponnesus and show that its nucleation rupture zone and aftershocks sequence are confined to one slab panel between two adjacent along dip faults and are thus controlled by not only the offshore slab top segmentation but also the upper plate sea bottom morphology

wide angle images of the mediterranean ridge backstop structure the mediterranean ridge is an accretionary wedge consisting of a large pile of tectonically deformed sediments in the past the mediterranean ridge has been interpreted as a prism related to hellenic subduction however geophysical evidence pasiphae cruise 1988 has indicated the presence of a high velocity body southward of the hellenic trench which was subsequently interpreted as an extended continental backstop during the recent imerse project coincident wide angle and normal incidence seismic data were collected over the ridge along the ne sw medriff corridor explora cruise 1994 the objectives of the imerse project were to acquire the seismic observations necessary for a high resolution structural model of the western mediterranean ridge including the structure of the newly interpreted continental backstop here we present the results of recent re modelling of two ship expanding spread seismic refraction data esp 8 and 9 recorded during the pasiphae cruise the modelling of these data has allowed an approximate constraint on the position of the juncture between the mediterranean accretionary complex and its buttress also presented are processing and modelling results of the recently acquired imerse wide angle data travel time modelling of these data has allowed the construction of six multi azimuth velocity depth models these models show the existence of high velocity material at depth p wave velocity 5 km s inferred to be extended backstop and constrain its southward extent all models show the presence of a messinian evaporite layer near the surface the evaporite layer is observed to vary in thickness from 0 to 2 0 km with the existence of local thickening and thinning due to depositional factors tectonism and salt dissolution in addition combined analysis of the wide angle velocity models with coincident seismic reflection and swath bathymetry data indicates that the geometry of the continental backstop varies laterally as a consequence of transform faulting possibly related to the southward rotation of the peloponnesus thrust sheet and backstop emplacement

nappe stacking resulting from subduction of oceanic and continental lithosphere below greece we quantitatively investigate the relation between nappe stacking and subduction in the aegean region if nappe stacking is the result of the decoupling of upper crustal parts 5 10 km thick from subducting lithosphere then the amount of convergence estimated from balancing the nappe stack provides a lower limit to the amount of convergence accommodated by subduction the balanced nappe stack combined with the estimated amount of completely subducted lithosphere indicates 700 km of jurassic and 2400 km of post jurassic convergence from seismic tomographic images of the underlying mantle we estimate 2100 2500 km of post jurassic convergence we conclude that 1 the imaged slab represents the subducted lithosphere that originally underlay the nappes 2 since the early cretaceous subduction in the aegean has occurred in one single subduction zone and 3 the composition of the original basement of the nappes indicates that at least 900 km of sub upper crust continental lithosphere subducted in the aegean

evaluating temporal changes in hydraulic conductivities near karst terrain dams dokan dam kurdistan iraq summary dam sites provide an outstanding opportunity to explore dynamic changes in the groundwater flow regime because of the high hydraulic gradient rapidly induced in their surroundings this paper investigates the temporal changes of the hydraulic conductivities of the rocks and engineered structures via a thorough analysis of hydrological data collected at the dokam dam iraq and a numerical model that simulates the darcian component of the seepage analysis of the data indicates increased seepage with time and suggests that the hydraulic conductivity of the rocks increased as the conductivity of the grout curtain decreased conductivity changes on the order of 10 8 m s in a 20 yr period were quantified using the numerical analysis it is postulated that the changes in hydraulic properties in the vicinity of dokan dam are due to suspension of fine materials interbedded in small fissures in the rocks and re settlement of these materials along the curtain consequently the importance of the grout curtain to minimize the downstream seepage not only as a result of the conductivity contrast with the rocks but also as a barrier to suspended clay sediments is demonstrated the numerical analysis also helped us to estimate the proportion of the disconnected karstic conduit flow to the overall flow

moho topography under central greece and its compensation by pn time terms for the accurate location of hypocenters the example of the gulf of corinth 1995 aigion earthquake abstract in this paper we expand over the whole of central greece the moho map centered on the gulf of corinth from tomographic inversion of pmp traveltime profile data recorded by several tens of temporary stations our approach is based on pn moho refracted waves from a large regional earthquake recorded by both temporary stations and the permanent hellenic network the moho map shows the large moho depth under the hellenides belt it also highlights the shallower moho domain towards the aegean sea south and east of the corinth gulf the domain of shallow moho is limited along a ne sw prolongation ahead of the north anatolian fault from the north aegean trough to the western tip of the gulf of corinth towards the gulf of patras the pn time terms provide corrections for the permanent stations that can be used together with the 1d velocity depth model for a first order compensation of lateral heterogeneity and contribute to the accurate and fast location of earthquake hypocenters as a test we relocated the 1995 aigion earthquake in this way using only the sparse data of the permanent stations hypocentral coordinates then shift close to those derived by a dedicated dense array deployed after the earthquake implying improvement of the routine location

seismic coupling and structure of the hellenic subduction zone in the ionian islands region abstract the western hellenic arc has been commonly considered as a largely aseismic subduction zone from the comparison of a small rate of shortening derived from the seismic moment release with a large rate of convergence inferred from geology complete seismic coupling would instead be expected from models that consider a control by plate tectonic forces because of the trenchward velocity of the hellenic aegean upper plate now confirmed with gps measurements in the region of the ionian islands a subduction interplate boundary has been recently imaged and its seismogenic downdip width suggested to be moderate from reflection seismic profiling and local earthquake tomography in the appropriate model for such an earthquake source region which considers a single interplate fault and takes into account these features the moderate seismic moment release is found consistent with complete seismic coupling of this subduction the shallow downdip limit of the seismogenic zone can be interpreted as due to the interplate boundary being overlain there by the ductile deeper crust of the orogenically thickened hellenides

s wave velocities of the lithosphere asthenosphere system in the lesser antilles from the joint inversion of surface wave dispersion and receiver function analysis abstract we present an overview of s wave velocities vs within the crust and upper mantle of the lesser antilles as determined with 19 seismic broadband stations receiver functions rf have been computed from teleseismic recordings of earthquakes and rayleigh wave group velocity dispersion relations have been taken from earlier surface wave tomographic studies in the caribbean area local smoothness optimization lso procedure has been applied combined with an h k stacking method the spatial distribution of hypocenters of local earthquakes and of the energy they released in order to identify an optimum 1d model of vs below each station several features of the caribbean plate and its interaction with the atlantic subducting slab are visible in the resulting models a relatively thick oceanic crust below these stations ranges from 21 km to 33 km being slight thinner in the middle of the island arc b crustal low velocity zones are present below stations saba seus ski smrt cbe dsd gcmp and tdba c lithospheric thickness range from 40 km to 105 km but lithosphere asthenosphere boundary was not straightforward to correlate between stations d the aseismic mantle wedge between the caribbean seismic lithosphere and the subducted slab varies in thickness as well as vs values which are in general lower below the west of martinique than below the west of guadeloupe e the depth of the subducted slab beneath the volcanic arc appears to be greater to the north and relatively shallower below some stations e g dlpl sam bim and fdf than was estimated in previous studies based on the depth distribution of seismicity f the wbz is 10 15 km deeper than the top of the slab below the central lesser antilles martinique and dominica where the presence of partial melt in the mantle wedge seems also to be more evident

seismic structure and the active hellenic subduction in the ionian islands in the region of the ionian islands of western greece the active margin of the hellenic domain passes from oceanic subduction in the south to continental collision in the north linked by the right lateral cephalonia transform fault a slightly landward dipping interface revealed at 13 km depth by a single previous line in the channel between cephalonia and zante has been suggested as the interplate subduction boundary new marine multichannel reflection profiles and obs refraction and wide angle reflection data confirm the reflector as a regional feature these data evidence its extension to the south where large low angle thrust earthquakes occur offshore to zante the new profiles establish a coincidence between the focal depths of these large subduction events and the imaged bright reflective level confirming its tentative interpretation as the interplate boundary which generally appears with a positive reflection polarity in this context the ionian islands outcrop corresponds to a shallowing of the interplate boudary from south to north in the south offshore zante the interplate boundary comprises a stratified zone that may be considered as the sedimentary cover of the ionian basin oceanic like crust which forms the lower plate here the shallower position and single cycle reflection character of the interplate further north suggest that the lower plate could there be the apulian paleomargin to that basin

fine scale gas distribution in marine sediments assessed from deep towed seismic data in the context of seismic imaging of gas gas hydrate systems the fine scale structure of subseabed gas related reflections is assessed by taking advantage of the source signature of the deep towed high resolution sysif seismic device we demonstrate the value of an original wavelet based method and associated multiscale seismic attributes applied to seismic data recently acquired on the western margin of the arctic archipelago of svalbard from analysis in the wavelet domain we recognize two types of gas related reflections associated with submetre scale distribution of gas we identify a thin gas charged layer associated with an apparent normal polarity reflection and we detect gas patches associated with a reverse polarity bright spot with frequency dependent elastic properties at small seismic wavelengths the results provide valuable information on the scale of features through which gas migrates and resolve ambiguities in the interpretation of the seismic data

contribution of spectral coherency analysis and tracer test to study leakage at the doosti dam reservoir iran and turkmenistan the doosti dam was built across the harirood river on the border between turkmenistan and iran during the reservoir impounding leakage occurred as new springs through the sandstone layers of the pesteleigh aquifer and limy sandstone and limestone layers of the neyzar kalat aquifer at the right abutment of the dam to evaluate the grout curtain operation a tracer test was carried out by injection of uranine in a borehole located at the upstream of grout curtain in the pesteleigh aquifer tracer test results demonstrated a diffuse flow component through the grout curtain in the pesteleigh aquifer but no tracer was detected at the main leakage point sp1 spring emerged downstream of grout curtain from the neyzar kalat aquifer using the spectral coherency function the lag time between changes in the water level of the injection borehole and water level in the tracer detected boreholes or discharge of the tracer detected springs was determined linear regression analyses indicated that the estimated lag time by the time series analysis was close to the first arrival time of the tracer therefore the estimated velocities based on the lag time of time series could be considered close to the calculated velocities based on the first arrival time of the tracer the estimated groundwater velocities based on the time series analysis ranged from 3 91 to 20 31 m h 1 showed that diffuse flow dominated pathways from the reservoir toward the downstream boreholes in the neyzar kalat aquifer while conduit flow was present within the pathways toward the sp1 spring regarding the reservoir volume the negligible amount of leakage at the maximum water level of the reservoir confirmed well overall operation of the grout curtain at the dam site

high resolution seismic imaging of the western hellenic subduction zone using teleseismic scattered waves summary the active hellenic subduction system has long been considered an ideal setting for studying subduction dynamics because it is easily accessible and of limited spatial extent it has been the focus of numerous seismological studies over the last few decades but nonetheless the detailed structure of both the slab and the surrounding mantle remain poorly constrained in an intermediate depth range from 30 to 150 km the objective of this paper is to fill this gap the intermediate depth regime is of particular interest because it is pivotal for improving our understanding of the dynamic interaction between subducting lithosphere and the surrounding mantle an interdisciplinary effort aimed at addressing this challenge is currently undertaken by the multidisciplinary experiments for dynamic understanding of subduction under the aegean sea medusa project as part of the medusa initiative a temporary array consisting of 40 densely spaced broad band seismometers from the iris passcal pool has been deployed in southern greece we process the teleseismic data recorded by this array with a migration algorithm based on the generalized radon transform to obtain high resolution images of the subduction zone in 2 d the images reveal a sharp mohoroviy discontinuity moho at depths ranging from 30 km beneath the western margin of the aegean sea to 40 km beneath the central peloponnesus where it outlines the crustal root of the hellenides to the west of the hellenides the continental moho is not identified but we interpret a pronounced discontinuity imaged at 20 km depth as the contact between low velocity sediments and high velocity crystalline basement the images also show the subducted oceanic crust as a low velocity layer that plunges at a constant angle of 21 from west to east the oceanic crust exhibits low velocities to at least 90 km depth indicating that the bulk of fluid transfer from the subducted slab into the mantle wedge occurs below this depth a detailed comparison of images constructed for distinct backazimuthal illuminations reveals deviations in the geometry of the subducted slab these deviations are attributed to structural and or compositional changes taking place directly to the north of the medusa array and are consistent with the existence of a slab tear beneath the central hellenic shear zone

receiver function study of the hellenic subduction zone imaging crustal thickness variations and the oceanic moho of the descending african lithosphere summary we use data from recently installed broad band seismographs on the islands of crete gavdos santorini naxos and samos in the hellenic subduction zone to construct receiver function images of the crust and upper mantle from south of crete into the aegean sea the stations are equipped with sts 2 seismometers and they are operated by gfz potsdam university of chania and eth zurich teleseismic earthquakes recorded by these stations at epicentral distances between 35 and 95 have been used to calculate receiver functions the receiver function method is a routinely used tool to detect crustal and upper mantle discontinuities beneath a seismic station by isolating the p s converted waves from the coda of the p wave converted p s energy from the oceanic moho of the subducted african plate is clearly observed beneath gavdos and crete at a depth ranging from 44 to 69 km this boundary continues to the north to nearly 100 km depth beneath santorini island because of a lack of data the correlation of this phase is uncertain north of santorini beneath the aegean sea moho depths were calculated from primary converted waves and multiply reflected waves between the moho and the earth s surface beneath southern and eastern crete the moho lies between 31 and 34 km depth beneath western and northern crete the moho is located at 32 and 39 km depth respectively and behaves as a reversed crust mantle velocity contrast possibly caused by hydration and serpentinization of the forearc mantle peridotite the moho beneath gavdos island located south of crete in the libyan sea is at 26 km depth indicating that the crust south of the crete microcontinent is also thinning towards the mediterranean ridge this makes it unlikely that part of the crust in crete consists of accreted sediments transported there during the present day subduction process which began approximately 15 ma because the backstop i e the boundary between the current accretionary wedge of the mediterranean ridge and the crete microcontinent is located approximately 100 km south of gavdos a seismic boundary at 32 km depth beneath santorini island probably marks the crustal base of the crete microcontinent a shallower seismic interface beneath santorini at 20 25 km depth may mark the depth of the detachment between the crete microcontinent and the overlying aegean subplate the moho in the central and northern aegean at naxos and samos is observed at 25 and 28 km depth respectively assuming a stretching factor of 1 2 1 3 crustal thickness in the aegean was 30 35 km at the inception of the extensional regime in the middle miocene

intraslab deformation and rupture of the entire subducting crust during the 25 october 2018 mw 6 8 zakynthos earthquake

disruption of the hellenic arc late miocene extensional detachment faults and steep pliocene quaternary normal faults or what happened at corinth 1 extensional faults exposed in the peloponnesus and mainland greece most of which are described here for the first time record a transition from regional extension of the aegean domain to the modern tectonic system the east peloponnesus detachment system trends north northwest from the southern peloponnesus to 30 km north of the gulf of corinth dips gently northeast and is late miocene early pliocene in age it has a minimum displacement of 25 30 km and appears to be the youngest of the regional scale extensional systems with significant displacement that formed parallel to the hellenic arc the partially coeval east sterea extensional system which extends from the gulf of corinth to the aegean sea contains low angle normal faults that both crosscut and trend parallel to older structures of the hellenic arc late miocene to early pliocene displacement within this zone disrupted the arc parallel structures of the hellenides upper pliocene quaternary normal faults which trend approximately east west and generally dip steeply at the surface continue the disruption of the hellenic arc much of the subsidence within the gulf of corinth appears to be unrelated to the younger faults and is instead related to the motion on the east peloponnesus detachment which crosscuts the modern graben

interaction between a dam site and karst springs the case of supramonte central east sardinia italy abstract sardinia is one of the italian regions with the greatest number of dams per inhabitants almost 60 for a population of only 1 5 million people many of these dam sites are located on non carbonate rocks along the main rivers of the island and their waters are used for irrigation industrial energy supply drinking and flood regulation purposes the pedra e othoni dam on the cedrino river dorgali central east sardinia is located along the threshold of the palaeozoic basement on the northern border of the supramonte karst area where water is forced to flow out of the system through several resurgences the most famous of which is the su gologone vauclusian spring used for drinking water supply the other main outflows of the system su tippari and san pantaleo springs are at present almost permanently submerged by the high water level of the pedra e othoni dam in the near future water will be supplied also to other communities with a possible increase of water taken from the spring the dam originally meant to regulate the flooding of cedrino river but actually used for all sorts of purposes electricity supply drinking water irrigation of farmlands industrial uses has a maximum regulation altitude of 103 m a s l only slightly less than a meter below the su gologone spring level 103 7 m and 4 and 9 m respectively above the submerged su tippari and san pantaleo springs during floods of the cedrino river occurring on average twice a year also the su gologone spring becomes submerged by the muddy waters of the lake for a time ranging between a couple of hours up to several days making water supply impossible the analysis of the available meteorological and hydrogeological data relative to the december 2004 flood one of the severest of the past 100 years suggests that the reservoir is filled in a few days time several flooding scenarios have been reconstructed using digital terrain models showing that backflooding submerges most of the discharge area of the aquifer having important repercussions also on the inland underground drainage system the upstream flood prone areas prevalently comprise agricultural lands with some sparse houses but also highly frequented tourist facilities fortunately flooding occurs outside the tourist season thus limiting risk to a limited number of local inhabitants massive discharge at the dam site instead determines a more hazardous situation in the cedrino coastal plain where population density in low lying areas is much higher to avoid flooding hazard upstream the water level in the lake should be regulated keeping it low in the flood prone seasons and having it filled from the end of the winter in order to have enough water stocked before the beginning of the summer discharge at the dam site instead should be done cautiously preventing severe flooding of the coastal cedrino plain

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

multiscale seismic attributes source corrected wavelet response and application to high resolution seismic data a wavelet based method was presented in a previous work to introduce multiscale seismic attributes for high resolution seismic data because of the limited frequency bandwidth of the seismic source we observed distortions in the seismic attributes based on the wavelet response of the subsurface discontinuities le gonidec et al in this paper we go further in the seismic source correction by considering lalpha stable distributions introduced in the formalism of the continuous wavelet transform cwt the wavelets are gaussian derivative functions gdf characterized by a derivative order we show that a high resolution seismic source after a classical signature processing can be taken into account with a gdf we demonstrate that in the framework of the born approximation the cwt of a seismic trace involving such a finite frequency bandwidth can be made equivalent to the cwt of the impulse response of the subsurface and is defined for a reduced range of dilations we apply the method for the sysif seismic device marsset et al k eret al and show that the source corrections allow to define seismic attributes for layer thicknesses in the range 24 115 cm we present the analysis for two seismic reflectors identified on a sysif profile and we show that the source corrected multiscale analysis quantifies their complex geometries

a detailed receiver function image of the upper mantle discontinuities in the japan subduction zone abstract we have imaged the upper mantle discontinuities in a 30 20 large region at the active continental margin of the japan subduction zone and neighboring areas using p to s converted phases from teleseismic records of permanent broadband stations the 410 km discontinuity is detected within 10 km of its global average position an interesting exception in its observation is a gap near 135 e very close to the slab penetration of the 410 km discontinuity and in an area where we have rather high data density the 660 km discontinuity reaches 700 km depth at two places where it is hit directly by the slab these data generally show good agreement with tomographic results both the 660 km discontinuity depression and the p velocity anomalies suggest about 400 500 k temperature deficit within the slab however no downward bending of the 660 km discontinuity is observed in eastern china where the flat lying slab is imaged by tomography this suggests that the slab does not cool the 660 km discontinuity in this region therefore the positive buoyancy required to keep the slab lying flat cannot have been provided by the negative clapeyron slope of the spinel perovskite phase transition another mechanism is needed which could possibly be metastable olivine in the cold core of the slab we have also imaged the shallower portion of the slab down to about 150 km underneath some seismic stations likely because metastable gabbro is still existing to this depth providing a sufficient velocity contrast a strong negative converted phase is observed at 150 200 km depth underneath a volcanic region in japan if real observed at one station only the zone which produces this conversion and which may begin exactly above the slab would require fluid fed melting

identification of leakage and potential areas for internal erosion combining ert and ip techniques at the negratin dam left abutment granada southern spain abstract at the negratin dam southern spain two main springs derived from the water reservoir were detected on the west side of the mountain ridge matching the location of the left abutment of the dam the seepages appear when the level of the stored water exceeds 622 m above sea level m a s l where some paleochannels are embedded in the silts the water level was at 631 m a s l on the day of the measurements 13 12 23 close to the historical maximum 633 78 m a s l although the water crossing the leaks does not drag particles nowadays this sector may potentially cause internal erosion or piping phenomena implying a loss of water resources and slope instability problems the infiltration areas were evaluated by electrical resistivity and induced polarization methods measured along one profile on the mountain ridge between the water reservoir and the springs we determine that the infiltrations zones are characterized by low resistivity and high chargeability distributed in small areas we demonstrate that these methods are a reliable tool to detect and characterize infiltration zones and they are the first step to planning mitigation actions to avoid the piping phenomena

moho depth and poisson s ratio in the western central alps from receiver functions summary current knowledge about deep crustal structure of the alpine orogen has mainly been derived from p wave velocity models obtained from active and passive seismic experiments a complementary s wave model to provide lithological constraints necessary for unique structural interpretation has been missing to date in this paper we present important new information on s wave velocity model in the alps we applied the receiver function method using 6 yr of high quality data from 61 permanent and temporary stations sampling the western central alps we determined first order crustal features moho depth h and average vp vs ratio with the h stacking technique that uses timing of direct and multiple p to s converted phases from the moho interface synthetic tests reveal a dipping moho interface expected beneath an orogen causes a systematic bias of h and potentially leading to misinterpretation we thus applied corrections determined from synthetic data to remove the bias providing better fit of recovered moho depths with active seismic estimates for each site we also obtained independent h and estimates based on the timing of the strong ps phase our results show a gently south southeast dipping european moho at a depth of 24 30 km beneath the northern alpine foreland steepening rapidly towards the europe africa suture zone to reach a maximum depth of 55 km south of the suture the moho of the adriatic crust promontory of the african plate is at 35 45 km depth in the previously ill constrained western alps we found the european moho at 30 km depth beneath the more external units dipping east northeast to reach 50 55 km in the inner core of the alps the poisson s ratio clearly correlates with the tectonic units that comprise the alps average crustal values in the european alpine foreland are close to 0 25 in the alps we observe low values 0 22 in the highly deformed nappes of the mesozoic helvetic and southern alps indicating a thickening of felsic upper crustal material in contrast the poisson s ratio is significantly higher 0 26 in the penninic and austroalpine units near the suture zone this rapid and significant change marks a clear rupture between the alpine forelands and the suture domain we assign this high poisson s ratio to doubling of mafic lower crust consistent with results from previous active seismic experiments a continuation of the lower crustal wedge into the central part of the western alps however seems unlikely based on low observed poisson s ratios

seismic evidence for deep water transportation in the mantle we report seismic evidence for the transportation of water into the deep mantle in the subduction zone beneath northeastern japan our data indicate that water is released from the hydrated oceanic crust at shallow depths approximately 100 kilometers and then forms a channel of hydrated mantle material on top of the subducting plate that is the pathway for water into the deep mantle our result provides direct evidence that shows how water is transported from the ocean to the deep mantle in a cold subduction zone environment

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

slab top dips resolved by teleseismic converted waves in the hellenic subduction zone the variations of the arrival times and polarities with backazimuth and distance of teleseismic p to s converted waves at interfaces bounding the slab crust under the upper plate mantle are used to constrain the depth dip angle and azimuth of the slab of the hellenic subduction zone a grid search is designed to estimate the model parameters dip values of 16 18 with an azimuth of 20 to 40 are thus derived at 3 sites aligned over 50 km along the eastern coast of peloponnesus they are consistent with the variation from 54 to 61 km of the slab top depths constrained below each receiver north of the gulfs of corinth and evvia a similar depth for the top of the slab is found at a distance from the subduction at least 100 km larger this suggests flatter subduction of a different slab segment such a variation in slab attitude at depth across the region from south of the eastern gulf of corinth to north of evvia is a candidate for the control of the recent or active localized crustal thinning of the upper plate we documented in earlier work and of the surface deformation

elasticity of serpentines and extensive serpentinization in subduction zones 1 elastic constants of lizardite mg3si2o5 oh 4 were computed using first principles quantum mechanical calculations within the density functional theory the predicted c axis compressibility is much larger than measured modeling of the weak o h o interactions between layers must be improved in order to better predict layered hydrated mineral elastic properties the large computed bulk modulus range is consistent with equation of state and seismic velocities in chrysotile lizardite serpentinites but shear wave velocities are lower than the lowest theoretical estimate the low seismic velocities measured for chrysotile serpentinites can be attributed to specific contribution of the nanotube textured chrysotile for antigorite the data from acoustic and eos measurements are consistent if used for interpreting seismic velocities the inferred degrees of serpentinization of the mantle wedge are higher than with the commonly used calibrations using chrysotile serpentinite properties serpentine is likely a dominant phase in low velocity areas of the mantle wedge at 30 50 km depths

seismic facies characterization by monoscale analysis relating sedimentary records to seismic data is a major challenge by shifting focus to a scale invariant sharpness characterization for the reflectors we develop an attribute that can capture and categorize the main reflector features without being sensitive to amplitudes sharpness is defined by a scale exponent which expresses singularity order and determines the reflection signature waveform local scale exponent estimates are obtained with a new monoscale method compared to multiscale wavelet analysis our method has the advantage of measuring transition exponents at a single fixed scale using a simple on off criterion the exponents contain amplitude variation information and describe lithological onsets we create an image of the earth s local singularity structure by applying our method to seismic traces and well log data the singularity map facilitates interpretation facies characterization and integration of well and seismic data

new constraints on subduction zone structure in northern cascadia summary a detailed passive seismic experiment was carried out across southwestern british columbia and northwestern washington to investigate the structure of the subducting juan de fuca plate and mantle wedge in cascadia and its relation to intraslab seismicity as part of the polaris project 31 three component broad band stations were deployed in an approximately linear array spanning southern vancouver island the gulf and san juan islands watcom county and the british columbia lower mainland p wave coda from 41 teleseismic events have been employed in formal inversions for fine scale shear velocity structure our results indicate a structure very similar to that identified across a comparable profile in central oregon the continental moho is evident at the eastern end of the profile near 35 km depth but disappears towards georgia strait puget sound a prominent low s velocity zone is clearly evident below southern vancouver island dipping eastwards through georgia strait puget sound and coincides with the e reflection zone originally identified in lithoprobe studies structure below the e layer is much less prominent and varies intermittently along the array based on the observations and interpretations of similar structures beneath oregon alaska and south america and its projection to mantle depths we suggest that the low velocity e layer represents the dehydrating oceanic crust of the subducting juan de fuca plate this interpretation is consistent with recent seismicity studies that place shallow wadati benioff events within the oceanic mantle and implies that the oceanic crust is 6 8 km shallower beneath vancouver island than previously assumed as in oregon we interpret the diminished signature of oceanic crust below a depth of 45 km to signal the presence of eclogitization which in turn supplies water to serpentinize the overlying forearc mantle

fractional integration of seismic wavelets in anelastic media to recover multiscale properties of impedance discontinuities multiscale seismic attributes based on the wavelet transform properties have been recently introduced and successfully applied to identify the geometry of a complex seismic reflector in an elastic medium in the present paper we extend this quantitative approach to anelastic media where intrinsic attenuation modifies the seismic attributes and thus requires a specific processing to retrieve them properly the method assumes both an attenuation linearly dependent with the seismic wave frequency and a seismic source wavelet approximated with a gaussian derivative function we highlight a quasi conservation of the gaussian character of the wavelet during its propagation we show that this shape can be accurately modeled by a gaussian derivative function characterized by both a fractional integration and a frequency shift of the seismic source and we establish the relationship between these wavelet parameters and q based on this seismic wavelet modeling we design a time varying shaping filter that enables

simultaneous inversion of reflection and refraction seismic data and application to field data from the northern rio grande rift summary an inversion scheme that determines a velocity model simultaneously from normalincidence reflection and refraction wide angle reflection seismic data has been developed tested and applied to real seismic data simultaneous inversion minimizes the non uniqueness of inversion results a common midpoint cmp stacked reflection section provides a detailed image of the structural configuration in time refraction or wide angle reflection data can be used to derive a velocity model if both refraction data and normal incidence reflection data are available along coincident profiles simultaneous inversion of the data sets can produce an improved model with the extra control of the interface depth provided by reflection data it is also possible to avoid ambiguity of phase identification the commonly used damped least squares dls inversion method often results in significant inversion artefacts we provide effective methods for reducing inversion artefacts using both damping and smoothing from tests using synthetic data we conclude that the simultaneous inversion scheme can improve resolution and can be applied to velocity models with a reasonably complex structure the simultaneous inversion scheme has been successfully applied to coincident seismic reflection and refraction data recorded by the sage program in 1990 1991 in the western boundary area of the rio grande rift near abiquiu new mexico in this example the simultaneous inversion derived a velocity model in which stratigraphic units and extensional fault blocks can be resolved

crustal motion and deformation in greece from a decade of gps measurements 1993 2003 abstract the hellenic plate boundary region located in the collision zone between the nubian arabian and eurasian lithospheric plates is one of the seismo tectonically most active areas of europe during the last 15 years gps measurements have been used to determine the crustal motion in the area of greece with the aim to better understand the geodynamical processes of this region an extended reoccupation network covering whole greece has been measured periodically in numerous gps campaigns since the late eighties and a continuous gps network has been operated in the region of the ionian sea since 1995 in this paper we present a new detailed high quality solution of continuous and campaign type measurements acquired between 1993 and 2003 during the gps processing a special effort was made to obtain consistent results with highest possible accuracies and reliabilities data of 54 mainly european igs and euref sites were included in the gps processing in order to obtain results which are internally consistent with the european kinematic field and order to allow for a regional interpretation after an overview of the results of the igs euref sites the results from more than 80 stations in greece are presented in terms of velocities time series trajectories and strain rates previous geodetic geological and seismological findings are generally confirmed and substantially refined new important results include the observation of deformation zones to the north and to the south of the north aegean trough and in the west hellenic arc region arc parallel extension of about 19 mm yr along the hellenic arc and compression between the ionian islands and the greek mainland due to continuous long term observations of 4 8 years it was possible to extract height changes from the gps time series in greece we observe a differential subsidence of the order of 2 mm yr between the northern and central ionian islands across the kefalonia fault zone the differential subsidence of the central ionian islands with respect to the northwestern greek mainland amounts to 4 mm yr

a traverse of the ionian islands front with coincident normal incidence and wide angle seismics abstract marine vertical reflection profiling with a powerful airgun source augmented with a few wide angle seismometer stations on land has been applied along a 180 km line across the presently active deformation front of the subduction of the ionian sea plate beneath the western hellenides east of the ionian islands there is limited evidence for reflectivity down to 23 km interpreted as the base of a rather thin continental type crust under the western slope of the islands a major normal incidence reflector dips eastward first gently to the west of the islands then more steeply under them this reflector may be extrapolated southwestwards beneath a bulge that is thought to represent the modern pre apulian front located over the subduction zone the continuity signature and geometry of this reflector suggest that it may act as the lower limit of the western hellenides where they override the ionian sea quasi oceanic crust rather than just an intracrustal interface of a pre apulian crust the location of the previous deformation front the ionian thrust proposed in previous models can be constrained by the new seismic data the new data raise the possibility of a larger area of evaporite mobility than previously considered insofar as active block motion apparently related to halokinesis is recognized west of the zakynthos anticline diapirism decollement and westward directed over thrusting in the pre apulian crust may have been brought on by late pliocene quaternary reactivation of regional extension associated with the separation of the peloponnesus from northern greece as it was captured by the anatolian aegean rotation and associated also with the fast clockwise rotation of the ionian islands as they were sheared off the apulian domain to the southwest by the initiation of the kefallinia transform

multiscale seismic attributes a wavelet based method and its application to high resolution seismic and ground truth data we propose a wavelet based method to characterize acoustic impedance discontinuities from a multiscale analysis of seismic reflected waves our approach relies on the analysis of ridge functions which contain most of the information of the wavelet transform in a sparse support this method falls in the framework of the wavelet response wr introduced by le gonidec et al which analyses the impedance multiscale behaviour by propagating dilated wavelets into the medium we further extend the wr by considering its application to broad band seismic data we take into account the bandpass filter effect related to the limited frequency range of the seismic source we apply the method to a deep water seismic experiment performed in 2008 during the erig3d cruise to demonstrate the potential of ridge functions as multiscale seismic attributes in conjunction to the analysis of seismic data acquired by the deep towed sysif system 200 2200 hz we use ground truth data to characterize the fine scale structure of superficial sediments by using the continuous wavelet transform cwt the availability of in situ measurements allows to validate the relationship between cwt andwr and to estimate the attenuation of seismic waves into the sediments once validated the method is applied on a whole seismic profile and wr ridge functions are computed for two particular reflectors the reflector thicknesses fall below the resolution limit of the seismic experiment making the wr seismic attributes a super resolution method

lithospheric structure of the aegean obtained from p and s receiver functions combined p and s receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the aegean region are used to map the geometry of the subducted african and the overriding aegean plates we image the moho of the subducting african plate at depths ranging from 40 km beneath southern crete and the western peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern greece however the dip of the moho of the subducting african plate is shallower beneath the peloponnesus than beneath crete and rhodes and flattens out beneath the northern aegean observed p to s conversions at stations located in the forearc indicate a reversed velocity contrast at the moho boundary of the aegean plate whereas this boundary is observed as a normal velocity contrast by the s to p conversions our modeling suggests that the presence of a large amount of serpentinite more than 30 in the forearc mantle wedge which generally occurs in the subduction zones may be the reason for the reverse sign of the p to s conversion coefficient moho depths for the aegean plate show that the southern part of the aegean crustal thickness of 20 22 km has been strongly influenced by extension while the northern aegean sea which at present undergoes the highest crustal deformation shows a relatively thicker crust 25 28 km this may imply a recent initiation of the present kinematics in the aegean western greece crustal thickness of 32 40 km is unaffected by the recent extension but underwent crustal thickening during the hellenides mountains building event the depths of the aegean moho beneath the margin of the peloponnesus and crete 25 28 and 25 33 km respectively show that these areas are also likely to be affected by the aegean extension even though the cyclades crustal thickness of 26 30 km were not significantly involved in this episode the aegean lithosphere asthenosphere boundary lab mapped with s receiver functions is about 150 km deep beneath mainland greece whereas the lab of the subducted african plate dips from 100 km beneath crete and the southern aegean sea to about 225 km under the volcanic arc this implies a thickness of 60 65 km for the subducted african lithosphere suggesting that the aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the cyclades

treatment of the seepage problems at the kalecik dam turkey abstract this paper describes the seepage prevention measures at kalecik dam water leaked from the foundation of the dam after the impoundment the dam 77 m in height was constructed for irrigation purposes the foundation consists of mesozoic ophiolite paleocene allochthonous units composed of different lithologies and miocene conglomerate karstified and fractured paleocene limestone outcrops on the right bank of the dam foundation this unit extends into and its thickness increases within the right abutment the leakage occurs towards the downstream springs through the right bank limestone the main grout curtain is 200 m long and 60 m deep and was constructed on the right bank after reservoir impounding new springs were observed in the downstream area therefore after the construction of the dam remedial curtain grouting was required and carried out in three stages firstly the main grout curtain was supplemented by additional grouting to seal the fractures and infill karstic cavities the diversion tunnel was also repaired the curtain depth was the same as the depth of the previous curtain the second stage of additional treatment consisted of new deep grouting some investigation holes were also drilled along the same alignment as the main curtain to locate the seepage in the region these holes were extended to an elevation of 442 m the final stage of grouting measures was between the spillway and the dam body and underneath the spillway as a result of the additional grouting measures the spring discharges observed downstream of the dam embankment decreased however the seepage paths were extended and were moved with time so that the seepage problems are still continuing

seepage problems in the karstic limestone foundation of the kalecik dam south turkey abstract seepage phenomena through the karstic limestone foundation of kalecik dam are investigated the dam designed as a rock fill dam with a height of 77 m is already used for irrigation the foundation consists of mesozoic ophiolite paleocene allochthonous units composed of different lithologies and miocene conglomerate the conglomerate lies unconformably on the other units quaternary basaltic lava patchily covers the others seepage from upstream to downstream occurs through the allochthonous karstic limestone this limestone which is overlain by conglomerates has a thickness increasing towards the right abutment to prevent seepage at the right abutment a 200 m long and 60 m deep grout curtain along the dam axis was constructed after the impoundment some springs occurred downstream and for this reason extra grouting was performed however the seepage problem could not be solved in order to determine the seepage direction and karstification pattern hydrological studies have been done additional investigation boreholes have been drilled to observe fluctuations of the groundwater level and to analyze hydrochemistry also dye tracer tests have been carried out as a result of these hydrogeological studies seepage paths were observed in the karstic limestone located between the dam and the spillway as those carbonate rocks continue beneath the spillway the seepage problems are enjected to continue

evaluation and rehabilitation of dam seepage problems a case study kafrein dam abstract the intention of this study is to locate the probable sources of the kafrein dam seepage problem a methodology known as excitation response analysis will be considered analytical expressions depicting the groundwater level response in the underlying aquifer as a result of changes in the reservoir water level were derived from a linearized groundwater flow equation for one dimensional semi infinite isotropic and homogeneous porous media the results revealed that a large proportion of the seepage water originates from a site at a distance about 1 km from the observation point m1 and streamlines along the existing faults emphasis in this work was also placed on controling and mitigating the seepage problem

wavelet transform a tool for the interpretation of upper mantle converted phases at high frequency p to s converted receiver functions recorded at vbb fdsn california stations are studied in the frequency range of 0 1 to i hz microseismic noise is maximum in this frequency range but signal processing by the wavelet transform enables us 1 to enhance seismic phases associated with seismic velocity gradients and discontinuities at the base of the upper mantle 2 to extract accurate arrival times and 3 to obtain an accurate insight into the frequency content in the case of california one seismic discontinuity and two zones of high gradients in the depth range of 625 to 720km are recurrently observed for two different data sets

seepage problems in the right abutment of the shahid abbaspour dam southern iran abstract in this study seepage phenomena through the right abutment of shahid abbaspour dam are investigated the shahid abbaspour dam is a 200 m high arch dam which regulates the waters of the karun river serves power generation and flood control and irrigation needs the dam site lies in the zagros mountains of southern iran this region presents continuous series of mainly of karstic limestone marl shale and gypsum ranging in age from jurassic to pliocene the region has subsequently been folded and faulted seepage from the shahid abbaspour reservoir occurs mainly through the karstic limestone the basic foundation treatment of the dam consisted of consolidation grouting a high pressure grout curtain and a drainage curtain moreover a 144 m high and 30 m wide concrete cutoff wall was built to prevent reservoir seepage through a clay filled fracture zone in the right abutment the grout curtain penetrates the principal vuggy zone only beneath the central portion of the dam and below the cutoff wall in the right abutment fan curtains were constructed to reduce drainage flows but the seepage problem could not be solved in order to determine the seepage direction and karstification pattern hydrogeological studies have been carried out additional investigation boreholes have been drilled to monitor fluctuations in groundwater level besides these water chemistry dye tracer pinhole and xrf tests have been carried out as a result of these studies seepage paths have been identified in the karstic limestone in the right abutment of the dam

methoni mw 6 8 rupture and aftershocks distribution from a dense array of obs and land seismometers offshore sw hellenic subduction abstract along the south western offshore hellenic subduction zone the overriding aegean upper plate above the mediterranean oceanic lithosphere generates uncommon large earthquakes on the offshore megathrust fault the largest subduction thrust event for half a century has been the 14 february 2008 methoni earthquake mw 6 8 that occurred offshore of the southwest coast of peloponnesus we conducted micro seismicity experiments around the rupture area and forearc domain between peloponnesus and crete using ocean bottom seismometers obs jointly with land based seismological stations our first experiment in 2006 had revealed an association of the matapan trough a 400 km long forearc basin with local seismicity clustering and a possible gap in activity over the later methoni rupture area here we present new data of post methoni seismic activity recorded during a time span of 11 months beginning in october 2008 within the period of proposed afterslip on the megathrust by an extended and dense seismic array consisting of up to 33 obs a minimum 1d velocity model was constructed for the region to provide better constraints on absolute locations and double difference relocation was applied to produce an enhanced image of the spatial distribution of hypocenters the high resolution earthquake locations confirm correlation of the matapan trough with local seismicity as a regional feature also filling up the previously observed gap over the methoni rupture area we constrain seismicity to be located mainly within the upper plate hypocenters are also resolved above the updip and downdip edges of the rupture area respectively seismic activity provides hints of upper plate structures which were activated in response to post seismic deformation spreading within the forearc crust our findings highlight the characteristics of a megathrust domain which is related with a highly deformable overriding plate and controlled by a segmented lower plate topography

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

the fate of the downgoing oceanic plate insight from the northern cascadia subduction zone abstract in this study we use teleseismic receiver function analysis to image the seismic structure of the juan de fuca oceanic plate during its subduction beneath the north american plate seismic data have been recorded at 58 seismic stations deployed along the northern cascadia subduction zone harmonic decomposition of the receiver function data set along a trench normal profile allows us to image both the isotropic and the anisotropic structure of the plate slab our images highlight the presence of a highly anisotropic region at 40 70 km depths across the cascadia subduction zone the detected seismic anisotropy is interpreted to be related to both metamorphic facies e g blueschists and fluid released during the dehydration of the subducting mantle the processes of dehydration and metamorphism produce the variations of the seismic properties within each lithologic unit that constitutes the subducted slab i e basalts gabbro layer and upper mantle as the oceanic plate sinks in the upper mantle such variations make it almost impossible to recognize the plate boundary as a characteristic velocity jump at depth neither positive nor negative along the cascadia subduction zone based on the comparative interpretation of both the isotropic and the anisotropic structures retrieved we propose a 4 stage model of the evolution of the juan de fuca oceanic plate during its subduction beneath the north american plate

evaluation and treatment of seepage problems at chapar abad dam iran engineering geological properties of the ground at the chapar abad dam were investigated in order to evaluate seepage problems and to select a proper method of water proofing prior to construction the dam is located to the northwest of iran and is undergoing construction phase the geology of the site consists of a series of early cambrian limestones and shales that crop out on the abutments and a valley that is filled by 60 m of alluvium deposits the presence of thick alluvium deposits with various coefficients of permeability along the foundation demonstrates a possible seepage problem after water impoundment in the reservoir the potential of water seepage was evaluated by the study of joint systems of the rock units the use of numerical analysis to simulate water flow in the ground and by conducting in situ tests to estimate the permeability s values based on the obtained results and by reviewing many types of water proofing methods regarding cost feasibility and safety factors the installation of a grout curtain is suggested

trench motion slab geometry and viscous stresses in subduction systems summary a semi analytic 3 d model for subduction within a newtonian viscous upper mantle provides a dynamically consistent means of computing viscous stress trench motion and slab geometry in subduction systems although negative slab buoyancy provides the basic driving force for subduction slabs that extend from the surface to the base of the upper mantle are oversupported by viscous stresses in the shallow 100 150 km mantle and undersupported by viscous stresses at greater depth in the upper mantle these deeper parts of the subduction system act as an engine for subduction while shallower parts act as a brake on trench motion trench migration rates and slab geometry reflect a competition between these two effects during steady state subduction trench migration rates vary approximately linearly with slab buoyancy and model rates of trench motion are in good agreement with the range of observed rates for a two layer upper mantle viscosity of 2 10 20 pa s above 300 km and 5 10 20 pa s below steady state slab dip increases as slab density decreases especially for very low density slabs which dip significantly more steeply than high density slabs the horizontal velocity at the top of the lower mantle measured relative to the foreland has a very large effect on trench migration rates rivalling or even exceeding that of slab buoyancy slab width parallel to the trench also has a significant effect on trench migration rates due to the viscous pressure of toroidal flow around the slab the stiffness of the subducting lithosphere does not exert a significant effect on trench migration rates or slab geometries for rigidities compatible with oceanic lithosphere very stiff slabs with elastic plate thicknesses more that 40 km or viscosities in the range of 10 25 10 26 pa s subduct significantly more slowly than weak slabs with trench migration rates in the range of half to a third that of weak slabs large unexpected effects on trench migration rates and slab geometry are exerted by the structure and density of the frontal prism and overriding plate indicating that local geology can exert important constraints on slab dynamics during non steady state subduction rates of trench migration respond rapidly as variably buoyant lithosphere penetrates into the asthenosphere in the absence of other driving forces for convergence trench migration rates can change by a factor of two or more in as little as 2 3 myr for example from 35 to 70 mm yr 1 when an oceanic piece of slab follows a continental one into the subduction system subduction of variable buoyancy lithosphere is accompanied by changes in slab dip with depth and through time

frontal accretion along the western mediterranean ridge the effect of messinian evaporites on wedge mechanics and structural style in the context of the imerse project several crossings of the deformation front of the western mediterranean ridge were made in the region of the sirte abyssal plain the messina abyssal plain and the intervening region in this paper we present seismic images and interpretations across the deformation front with particular emphasis on the role the messinian evaporites have played in controlling the accretionary tectonics of the thin frontal portion of the wedge the seismic images show that the basal detachment generally is located at the base of the evaporites from a consideration of the mechanics of the wedge for both coulomb and plastic rheologies we show that the low wedge taper c 2 requires that the detachment is characterised by extreme fluid overpressuring within 2 of lithostatic in places and that the basal yield stress less than 1 mpa is lower than that of a wet salt decollement zone this supports the seismic interpretation that the detachment occurs in overpressured sediments beneath the impermeable evaporites lateral variations in the accretionary style can be related to lateral variations in evaporite thickness the effectiveness of the evaporite as an impermeable seal and to local relief on the subducting plate these factors control the escape of fluids from beneath the evaporites and hence fluid pressure and basal yield stresses

earthquake mechanisms in the hellenic trench near crete summary in the hellenic trench south of crete convergence between the southern aegean sea and africa occurs at a rate of at least 60 mm yr 1 previously published first motion fault plane solutions show a variety of different fault orientations and types but are not well constrained furthermore the lack of reliable focal depths for these earthquakes has obscured any simple pattern of deformation that might exist nonetheless the mechanisms of these earthquakes have strongly influenced views of the tectonics in the hellenic trench we have improved estimates of the fault parameters and focal depths for 14 of these earthquakes using long period p and sh waveforms the earthquake mechanisms fall into four groups a normal faults with a n s strike in the over riding material above the subduction zone b low angle thrusts with an e w strike at a depth of about 40 km c high angle reverse faults with the same strike but shallower focal depths than b d events within the suducting lithosphere with approximately e w p axes the thrusting in groups b and c is probably the mechanism by which the sediments of the mediterranean sea underplate and uplift crete these events have slip vectors in the direction 025 12 which represents the convergence direction between crete and africa along the sw facing boundary of the hellenic trench one of the events in group d occurred beneath the mediterranean ridge and involved high angle reverse faulting with a wnw ese p axis almost perpendicular to the direction of shortening deduced from folds at the surface the mediterranean sea floor in this region appears to be in a state of e w compression for reasons that are not clear

the geometry of the wadati benioff zone and lithospheric kinematics in the hellenic arc abstract accurate locations of 961 shallow and intermediate depth earthquakes which occurred between 1956 and 1995 in the hellenic arc 34 39 n 19 28 e are used to define the plate boundaries in this area reliable fault plane solutions for 77 shallow and intermediate depth earthquakes are also used in order to define the interaction between the different plates in the arc an ocean continent type of interaction occurs on a curved surface which is defined by the shallow branch 20 100 km of the wadati benioff zone the intersection of this zone with the earth s surface is a curve which follows the convex outer side of the sedimentary arc western peloponnese west of cythera south coast of crete east coast of rhodes and dips at low angle 30 to the aegean sea coupling between the subducted oceanic crust and the overriding of the aegean lithospheric plate takes place on this surface the deep branch 100 180 km of the wadati benioff zone is dipping freely without coupling at a high angle 45 beneath the south aegean trough and the volcanic arc the high shallow seismicity h 20 km which is observed in the southwestern convex outer side of the arc ionian sea is attributed to the fast southwestward motion of the aegean plate location of strong deep earthquakes h 100 km in the fore arc area of the southwestern part of the hellenic arc west of cythera indicates that oceanic crust is destroyed in this part of the hellenic trench due to roll back of the descending lithospheric slab

two ship deep seismic soundings in the basins of the eastern mediterranean sea pasiphae cruise summary new results from a two ship refraction and oblique reflection deep seismic cruise are presented to discuss the nature of the crust in the ionian sirte and herodotus abyssal plains these expanding spread profiles were processed and analysed in both the x t and p domains arrival times of reflected and refracted branches are matched by ray tracing in both domains in spite of a shallow evaporitic sequence messinian evaporites deposited on top of a thick sedimentary pile responsible for velocity inversions on many profiles we obtain excellent velocity control down to moho depth pmp and pn 8 4 8 6 km s 1 arrivals are observed the three basins have a relatively thin crust 8 to 11 km overlain by a thick sedimentary cover up to 10km in the herodotus abyssal plain the moho boundary and main crustal units identified in the basins can be followed beneath the calabrian prism to the west and beneath the mediterranean ridge to the east the crustal structure is of oceanic type for both the ionian and sirte basins where typical oceanic layer 2 and 3 are recognized the thin crust of the herodotus basin may be interpreted either as oceanic or thinned continental crust about 10 km thick the top of the crust of the herodotus basin is much deeper therefore the herodotus basin is probably significantly older than the ionian basin triassic versus early cretaceous in age

accretion structural style and syn contractional sedimentation in the eastern mediterranean sea we analyse four multichannel seismic profiles collected by ogs from 1971 to 1979 along the outer part of the mediterranean ridge accretionary complex in order to understand the nature of the deformation affecting african plate sediments as they approach the africa europe plate boundary tectonic style as revealed by our data and previous studies varies considerably along the plate boundary and this variation suggests the division of the margin in three provinces characterised by different structural patterns and deformation rates 1 near orthogonal terminal subduction initial collision ionian and sirte foredeeps 2 incipient continental collision collision of continental promontories of the african margin off the cyrenaica peninsula 3 oblique terminal subduction initial collision herodotus foredeep this work aims to relate the tectonic features revealed by the seismic profiles to the geodynamic and stratigraphic parameters of the convergent margin these are essentially related to the geometry of subduction rate of convergence and obliquity and to the lithology of the incoming sedimentary section as well as the accumulation rate in the foredeep in the sirte province accumulation rate in the foredeep is relatively low and deformation is related to thrusting and folding which accounts for sediment shortening and uplift at the outer deformation front in the provinces of oblique terminal subduction the rate of normal convergence is lower the sedimentary section is thicker and the foredeep fed by the nile river has an higher syn tectonic sedimentation rate here deformation produces a broad band of large wavelength and high amplitude folds folding in this area is produced both by plate convergence related shortening and by movement of salt triggered by differential loading of the prograding nile deep sea fan in the area of incipient continental collision the foredeep is a v shaped trough as the abyssal plain has been completely subducted and the folded sediments of the accretionary complex rest directly on the african continental slope such differences in structural style are explained by great differences in strain rate that in the herodotus foredeep province has been calculated as at least four times weaker than in the western sector two factors contribute to decrease strain rate syn contractional accumulation and normal component of the effective convergence rate the former increases from west to east and possibly causes overpressuring on the decollement level salt mobilisation landward and seaward vergent folding and a very low surface taper in the herodotus foredeep the latter decreases from west to east and favours thrusting in the western sector

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

the lar dam an example of infrastructural development in a geologically active karstic region abstract the problems associated with the construction of the lar dam iran provide a classic example of problems that can result from infrastructural development in an active geological terrain which includes the regional carbonate units the lar dam lies in a heavily faulted and fractured region close to the active damavand volcano the fracturing has enhanced the production of karst and sinkholes in the limestone below the dam and acidic ground water run off from the damavand volcano increases the dissolution of the carbonate beds along the fractures to produce sinkholes below the dam the initial problem of building the dam in such a region is compounded by the relationship between water loss due to enhanced sinkhole development and the remedial measures being taken to lessen this leakage drainage of the sub reservoir caverns through leakage along fractures can lead to loss of hydrostatic support for the developing sub reservoir caverns and their consequent collapse furthermore rapid changes in subterranean water levels would lead to rock shattering hammer effects particularly during rapid rises in water level

segmented hellenic slab rollback driving aegean deformation and seismicity the ne dipping slab of the hellenic subduction is imaged in unprecedented detail using teleseismic receiver function analysis on a dense 2 d seismic array mapping of slab geometry for over 300 km along strike and down to 100 km depth reveals a segmentation into dipping panels by along dip faults resolved intermediate depth seismicity commonly attributed to dehydration embrittlement is shown to be clustered along these faults large earthquakes occurrence within the upper and lower plate and at the interplate megathrust boundary show a striking correlation with the slab faults suggesting high mechanical coupling between the two plates our results imply that the general slab rollback occurs here in a differential piecewise manner imposing its specific stress and deformation pattern onto the overriding aegean plate

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

hydrology and dynamics of a polythermal mostly cold high arctic glacier to improve our understanding of the interactions between hydrology and dynamics in mostly cold glaciers in which water flow is limited by thermal regime we analyse short term every two days variations in glacier flow in the ablation zone of polythermal john evans glacier high arctic canada we monitor the spatial and temporal propagation of high velocity events and examine their impacts upon supraglacial drainage processes and evolving subglacial drainage system structure each year in response to the rapid establishment of supraglacial subglacial drainage connections in the mid ablation zone a spring event of high horizontal surface velocities and high residual vertical motion propagates downglacier over two to four days from the mid ablation zone to the terminus subsequently horizontal velocities fall relative to the spring event but remain higher than over winter reflecting channelization of subglacial drainage but continued supraglacial meltwater forcing further transient high velocity events occur later in each melt season in response to melt induced rising supraglacial meltwater inputs to the glacier bed but the dynamic response of the glacier contrasts with that recorded during the spring event with the degree of spatial propagation a function of the degree to which the subglacial drainage system has become channelized copyright 2006 john wiley sons ltd

reflection refraction seismics in the gulf of corinth hints at deep structure and control of the deep marine basin abstract the gulf of corinth is a natural laboratory for the study of seismicity and crustal deformation during continental extension seismic profiling along its axis provides a 24 fold normal incidence seismic reflection profile and wide angle reflection refraction profiles recorded by sea bottom seismometers obs and land seismometers at wide angle incidence the land receivers document the moho at 40 km depth under the western end of the gulf north of aigion rising to 32 km depth under the northern coast in the east of the gulf both refraction and normal incidence reflection sections image the basement under the deep marine basin that has formed by recent extension the depth to the base of the sedimentary basin beneath the gulf constrained by both methods is no more than 2 7 km with 1 km of water underlain by no more than 1 7 km of sediment less than what was expected from past modeling of uplift of the south coast in the east of the gulf unlike the flat sea bottom the basement and sedimentary interfaces show topography along this axial line several deeps are identified as depocenters which suggest that this axial line is not a strike line to the basin it appears instead to be controlled by several faults oblique to the s60 e overall trend of the south coast of the gulf their more easterly strikes being consistent with the instantaneous direction of extension measured by earthquake slip vectors and by gps

an integrated hydrogeological approach to evaluate the leakage potential from a complex and fractured karst aquifer example of abolabbas dam iran the design and construction of dams are risky in karst regions with active tectonic settings and strong heterogeneity due to their leakage potential hydrogeological characterization by karst specific methods can be used to reduce the risk of improper dam construction numerous karstic dams have been constructed in the world in simple tectonic settings in this study a combination of geological and hydrogeological investigations is used with extensive data collection to evaluate the leakage potential of the abolabbas dam construction project at the malagha karst aquifer a tectonized highland karst region in the southwest of iran two thrust faults which bounded the malagha karst aquifer overthrusting caused extensive crushed zones continuous lengths with high permeabilities in most of the boreholes extensive open joints and small size solution cavities the results of artificial tracer tests imply that the flow regime is diffuse the flat water table diffuse flow regime extensive crushed zones and continuous high permeabilities most probably imply that the groundwater flows through an extensive network of joints without main conduits to drain the system despite a diffuse flow regime an extensive grout curtain both in length and depth is required to prevent leakage because the loose materials of the crushed zones will be washed out without it under high hydraulic gradients after dam impoundment the impermeable formation is too deep due to overthrusting therefore a huge leakage may occur under the hanging grout curtain the results allow a clearer understanding of the location and properties of fracture zones erodible materials high permeability zones groundwater flow regime and zones of preferential flow which are essential for reducing the failure of dam construction in such environments overall it is demonstrated that integrating different complementary methods can help to minimize the uncertainties inherent in engineering problems in similar karst scarce data regions

the gigantic seymareh saidmarreh rock avalanche zagros fold thrust belt iran the seymareh rock avalanche first described by j v harrison and n l falcon in the 1930s is the largest known subaerial non volcanic landslide on earth the volume of its debris 44 gm 3 is approximately equal to that of the largest known subaerial landslide of any kind the 100 ka collapse of mount shasta volcano 45 gm 3 and approaches those of gigantic landslides on mars using satellite imagery srtm 3 data and detailed field investigations we gain a new understanding of the gigantic rock avalanche the initial failure 38 gm 3 involving a dip slope consisting of a relatively weak interbedded limestone mudrock sequence capped by resistant asmari limestone had an average thickness of 410 m along a 15 5 km width of the kabir kuh anticline the rockslide transformed into a rock avalanche that travelled 19 0 km with a fahrboschung the angle between the highest point of the pre landslide source area topography and the distal limit of the debris of only 3 6 initial failure involved complex planar sliding dictated by four structural elements 1 bedding parallel shears and 2 across bedding break throughs combined to produce a low angle 11 overall sliding surface that 3 broke out through the asmari carapace at the toe of the failed slope while 4 tectonically weakened bedding normal joints provided lateral release surfaces nine discrete bedding parallel basal sliding surfaces divided the detached mass into nine stacked plates the upper plate 23 gm 3 included 20 7 gm 3 of asmari limestone analysis of accelerator mass spectrometry radiocarbon dates from this study and by others indicates that the rock avalanche occurred between c 8710 and 9800 14 c years bp supplementary material a summary of the tectonics stratigraphy and physiography of the zagros fold thrust belt together with a description of surficial gravity collapse structures in the region harrison falcon 1934 1936 is available at www geolsoc org uk sup18612

geodetic determination of the kinematics of central greece with respect to europe implications for eastern mediterranean tectonics we use a new satellite laser ranging global positioning system slr gps solution at seven sites in anatolia and aegea to obtain a better definition of the extrusion motion of the anatolian aegean block with respect to europe we show that this motion can be described in a first approximation by a counterclockwise rotation which transfers most of the motion of arabia to anatolia we combine 78 displacement vectors obtained at common points of two triangulation nets measured in central greece in 1895 and 1975 with the slr gps measurements to compute the velocity field over greece with respect to europe these measurements indicate that central greece is a zone of extension between the anatolian aegean counterclockwise rotation to the south and the northern greece clockwise rotation to the north this extension is principally localized within the gulf of corinth to the east but is distributed to the west we then extrapolate this velocity field to the whole aegea and western anatolia using recently published gps results as well as the slr results the narrow dextral north anatolian fault which limits the velocity field to the north progressively gives way to a much wider boundary zone where extension becomes dominant we show that the collision between the mediterranean ridge and africa began 3 6 ma and we describe the modifications that this collision has produced on the kinematic pattern both in aegea and on the mediterranean ridge