seismic source study of the racha dzhava georgia earthquake from aftershocks and broad band teleseismic body wave records an example of active nappe tectonics summary the racha dzhava earthquake ms 7 0 that occurred on 1991 april 29 at o9 12 48 1 gmt in the southern border of the great caucasus is the biggest event ever recorded in the region stronger than the spitak earthquake ms 6 9 of 1988 a field expedition to the epicentral area was organised and a temporary seismic network of 37 stations was deployed to record the aftershock activity a very precise image of the aftershock distribution is obtained showing an elongated cloud oriented n105 with one branch trending n310 in the western part the southernmost part extends over 80 km with the depth ranging from o to 15 km and dips north the northern branch which is about 30 km long shows activity that ranges in depth from 5 to 15 km the complex thrust dips northwards a stress tensor inversion from p wave first motion polarities shows a state of triaxial compression with the major principal axis oriented roughly n s the minor principal axis being vertical body waveform inversion of teleseismic seismograms was performed for the main shock which can be divided into four subevents with a total rupture time duration of 22s the most important part of the seismic moment was released by a gentle northerly dipping thrust the model is consistent with the compressive tectonics of the region and is in agreement with the aftershock distribution and the stress tensor deduced from the aftershocks the focal mechanisms of the three largest aftershocks were also inverted from body wave records the april 29th ms 6 1 and may 5th ms 5 4 aftershocks have thrust mechanisms on roughly e w oriented planes similar to the main shock surprisingly the june 15th ms 6 2 aftershock shows a thrust fault striking n s this mechanism is explai ned by the structural control of the rupture along the eastdipping geometry of the dzirula massif close to the borzhomi kazbeg strike slip fault in fact the orientation and shape of the stress tensor produce a thrust on a n s oriented plane nappe tectonics has been identified as an important feature in the caucasus and the source mechanism is consistent with this observation a hidden fault is present below the nappe and no large surface breaks were observed due to the main shock the epicentral region is characterized by sediments that are trapped between two crystalline basements the dzirula massif which crops out south of chiatoura and the caucasus main range north of oni most if not all of the rupture is controlled by the thrusting of overlapping deformed and folded sediments over the dzirula massif this event is another example of blind active faults with the distinctive feature that the fault plane dips at a gentle angle the racha range is one of the surface expressions of this blind thrust and its growtb is the consequence and evidence of similar earthquakes in the past ii 5

focal mechanisms and stress variations in the caucasus and northeast turkey from constraints of regional waveforms abstract the continental collision between arabia and eurasia created large strike slip faults in turkey as well as mountains in the caucasus and the volcanic plateau between them in this study we use regional waveforms of a new seismic array deployed between 2008 and 2012 to constrain the focal mechanisms and depths of small to moderate sized earthquakes occurring in the western part of the central caucasus and northeast turkey the distribution of aftershocks and the twelve focal mechanisms involved in the sequence of the 2009 earthquake in racha are clearly a reactivation of a deeper segment of the 1991 m7 racha rupture zone the deeper segment is not well connected to the shallower decollement separating the basement and sedimentary basin the earthquakes we determined in northeastern turkey and southern georgia are related to the strike slip fault system we further combined all of the reliably determined focal mechanisms over the last 30 years to investigate the current stress status of the crust in three areas racha in the western greater caucasus javakheti near the lesser caucasus and in northeast turkey our results show that the directions of maximum compressional stress consistently fall within 2 to 14 n throughout the entire study region this appears to be controlled by the continental collision nonetheless the minimum compression switches from vertical in the greater caucasus to the east west direction in northeastern turkey due to the westward extrusion of the anatolia block which is driven partly by the hellenic subduction the transition of the stress field is close to the javakheti volcanic plateau in the lesser caucasus where the relative magnitude between the principal stresses appears to be strongly variable

transition from a singly vergent to doubly vergent wedge in a young orogen the greater caucasus the greater caucasus mountains due to their youth 5 ma provide an opportunity for insight into the early stages of orogen development during continent continent collision however their recent tectonic evolution and first order architecture remain unclear here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity geodetic strain bedrock geology and foreland basin structure we find that the range contains four zones along strike that differ in structural architecture topography and first order tectonic history in particular two south directed singly vergent zones at the western and eastern tips of the orogen are separated by both a central doubly vergent zone that is dominated by north directed deformation and an eastern doubly vergent zone in which south directed thrusting dominates we hypothesize that the along strike changes in vergence and locus of deformation reflects different stages in the development of a doubly vergent orogen with the tips of the range preserving an early singly vergent form and the center recording a more advanced orogen the differences between the two doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the greater and lesser caucasus orogens which initiated at 5 ma

statistical analysis and clustering features of the phlegraean fields earthquake sequence may 1983 may 1984 abstract the seismic activity at the phlegraean fields volcanic area southern italy during the period may 1983 may 1984 5 301 selected events has been analyzed from a statistical point of view the analysis of the time series associated to the microearthquakes shows a high degree of interdependence among the events the main feature being the occurrence of dense swarms the generalized poisson process provides a good fit for the sequence the clustering of the events has not substantially changed during the analyzed period while the mean rate of occurrence of the swarms has generally increased the distribution of the magnitudes within the swarms shows pronounced maxima of energy around the center of the subsequences in agreement with theoretical models of fractures in highly heterogeneous media

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

inferences on the lithospheric structure of campi flegrei district southern italy from seismic noise cross correlation abstract lithospheric v s models are defined in the campi flegrei district southern italy through the non linear inversion of the group velocity dispersion curves of fundamental mode rayleigh waves extracted from ambient noise cross correlations between two receivers and the regional group and phase velocities of the italian cellular lithospheric model 1 1 cells four paths are investigated of which one ischia mis across two adjoining cells the distribution of v s shows a pyroclastic covering with v s increasing from 0 3 0 7 km s to 2 1 km s it rests on a lava or carbonate basement about 5 6 km thick with v s increasing from 2 1 km s to 3 1 km s at about 2 km of depth and rising to 0 6 km towards the island of procida a metamorphic layer is detected at an average depth of 7 7 km with v s of 3 8 3 9 km s about 5 km thick overlying a low velocity layer v s of 3 5 km s at about 11 12 km of depth the v s model along the ischia mis path as average of the models obtained by combining local and regional dispersion data of the two adjoining cells is well consistent with the other paths the moho discontinuity is retrieved at about 23 km of depth with v s of 4 2 km s

style and history of andean deformation puna plateau northwestern argentina topographically the puna plateau of northwestern argentina is the southern continuation of the bolivian altiplano its thickening and consecutive uplift result from the andean orogeny to better constrain the structural style and its progressive development we have studied field data topographic and satellite imagery balanced cross sections seismic reflection data kinematic analysis of fault slip data anisotropy of magnetic susceptibility ams paleomagnetic data and apatite fission track aft data across the puna plateau precambrian and paleozoic basement ranges bounded by high angle reverse faults dips 60 alternate with cenozoic intermontane basins major thrusts trend nne ssw and do not show a preferred vergence intermontane basins have various degrees of symmetry depending on the geometries and attitudes of associated thrusts as well as on the magnitudes of their offsets there is a close correlation between the surface expression of a basin and the amount of internal deformation a line balanced cross section of the puna at 25 s has yielded a cenozoic shortening of 10 15 in a direction subperpendicular to the orogen by kinematic analysis of cenozoic fault slip data we have obtained principal directions of strain rate across the puna shortening axes are subhorizontal and trend on average wnw ese n110 stretching axes are subvertical and intermediate axes are subhorizontal and trend on average nne ssw strain ellipsoids are dominantly of plane strain type and they represent dip slip thrusting from paleomagnetic and ams data shortening axes form a radial pattern around the eastern edge of the central andes the pattern is attributed to an inhomogeneous stress field reflecting the eastward convex shape of the central andean thrust front from the history of burial and uplift andean shortening reached the northeastern part of the puna in the late eocene and the adjacent eastern cordillera in the late eocene or early oligocene this shortening was presumably due to the incaic phase of the andean orogeny in the eastern part of the orogen the onset of shortening was probably guided by preexisting paleozoic and mesozoic structures so that andean deformation propagated unevenly eastward

mechanism of the 1992 erzincan earthquake and its aftershocks tectonics of the erzincan basin and decoupling on the north anatolian fault summary the 1992 march 13 erzincan earthquake ms 6 8 affected the erzincan basin on the eastern part of the north anatolian fault naf this event occurred on the eastern tip of a westward propagating series of major north anatolian earthquakes between 1939 and 1967 ambraseys 1970 it is located within a key region of eastern anatolia which displays both expulsion of the anatolian block towards the west and regional n s convergence due to the arabian eurasian collision philip et al 1989 a reinterpretation of the tectonics of the erzincan basin is made from field information and the analysis of satellite images a model explaining the development of the basin is proposed it combines a pull apart on the naf with the effect of two compressional wedges one is formed by the northeast anatolian fault neaf and the naf the other around pulumur is limited by the ovacik fault of and the naf both e w extension and n s compression occur according to this model normal faulting on the southwestern border and extension related quaternary rhyolitic volcanic domes along the northeastern boundary of the basin support the proposed e w extension the block limiting the southern side of the basin is uplifted and displaced left laterally along the of suggesting southward growth of the basin a kinematic model of the 1992 erzincan earthquake combines aftershock field information neotectonic observations satellite image interpretation and bodywaveform inversion the complex earthquake rupture starts on the naf and propagates bilaterally westward rupture propagation progresses along the northern border of the basin eastward propagation is shifted on a segment of the naf south of the euphrates and ends within the pulumur wedge both branches are connected by a system of normal faults the main focal mechanism is strike slip with a slight normal component o 122 63 164 the strongest aftershock mechanism is compatible with n s compression within the pulumur wedge aftershock mechanisms and stress tensor analyses give detailed insight into the earthquake sequence the 1992 erzincan earthquake is located between two segments of the naf that suffered large destructive earthquakes in the past the 1939 earthquake ms 8 2 ruptured 370 km west of erzincan the last major earthquake east of the erzincan basin occurred in 1784 rupturing a segment of at least 75 km length this area has displayed a seismic gap since then the mechanism of the main shock and the absence of aftershock activity east of tanyeri indicate decoupling between the 1992 event and the 1784 gap aftershocks within the pulumur wedge suggest that the probability of the occurrence of a future earthquake is higher on the of than in the 1784 earthquake gap

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

accurate fault mechanism determinations for a 1984 earthquake swarm at campi flegrei caldera italy during an unrest episode implications for volcanological research we have analyzed 42 microearthquakes 1 ml 3 that occurred at campi flegrei volcanic area during an intense swarm like activity more than 500 events in half a day in the last period of strong ground uplift 1982 1984 focal mechanisms of these earthquakes have been computed by a probability method which uses p wave polarity and s wave polarization data composite focal mechanisms for different groups of earthquakes have also been computed by the same technique results show a well defined fault plane in agreement with the elongation of the epicentral pattern the orientation and dip of this fault plane together with other observations about hypocenter locations and focal mechanisms of the whole seismicity accompanying the ground uplift episode suggest the presence of an elliptical fracture system at the caldera center this fracture system dipping toward the center of the caldera should represent the limit of the most recent caldera collapse which is also indicated by a negative bouguer gravity anomaly moreover an important differential feature among various groups of earthquakes has been shown namely a rotation up to about 30 of the strike of the compressive stress axis between the easternmost and the westernmost events the resulting pattern indicates that the axis is always oriented towards the town of pozzuoli which roughly represents the very center of the caldera and also the center of symmetry of the ground deformation these observations strongly suggest that earthquakes are generated by the variation of the stress field associated with the deformation along prefractured zones because of their greater weakeness this study provides then the first direct evidence that both seismicity and ground deformations have a common origin

surface wave tomography and seismic source studies at campi flegrei italy abstract we analyse a set of events recorded in march 1984 during a period of intense seismicity of the last bradyseismic crisis to determine shallow velocity models and seismic source moment tensors in the campi flegrei region the velocity models of the crust are obtained by surface wave tomography two inland negative anomalies of group velocity resulting in our tomographic maps well agree with previous independent measurements whereas a third anomaly located in the pozzuoli gulf and not evidenced by previous studies is in correspondence with the caldera position the inversion of the dispersion curves allows us to extend the already available velocity models within the uppermost 2 km of the crust the obtained models are employed to study seismic source features by the moment tensor analysis preliminary synthetic tests are performed in order to minimise artefacts in the moment tensor solutions possibly due to numerical noise to station distribution or to the structural modelling approximation most of the investigated earthquakes are deviatoric mechanisms and the increase of the isotropic component is observed in connection with the change of the seismicity rate in the investigated temporal window

the armenian earthquake of 1988 december 7 faulting and folding neotectonics and palaeoseismicity summary the spitak earthquake of 1988 december 7 is the first well documented event directly associated with surface breaks in the transcaucasian regions of the ussr the earthquake was located within the ese wnw oriented pambak sevan thrust and fold zone corresponding to the southern front of the lesser caucasus the mechanism of the earthquake is consistent with the nearly ns compressive tectonics due to the active continental collision between the arabian block and the russian platform the rupture is composed by several branches two of which reach the surface the first branch oriented n140 begins near the village of alavar has a length of 11 km and disappears at about 4 km se of spitak it consists of a right lateral en echelon system of strike slip faults with a maximum offset of 50 cm the second branch is the main one and breaks for about 8 km between spitak and gekhasar with a general orientation n120 showing reverse faulting dipping to the north with a right lateral component surface ruptures between gekhasar and spitak show either a narrow band of pressure ridges in alluvial deposits and soil or a fault scarp in the bed rocks when soil is absent maximum displacements observed between spitak and gekhasar attain 160 cm of vertical motion and 90 cm of horizontal dextral offset the displacement also varies within this branch showing finer segmentation few secondary deformations are observed some normal faults near gekhasar correspond to the collapse of the uplifted block an anticline fold oriented parallel to the fault scarp and situated along its northwestern prolongation emphasizes the regional compressive tectonics landslides were activated on its flanks a 200 m long reverse fault break observed along the hinge of a secondary fold suggests the occurrence of a blind thrust at depth and that the hidden branches which continue the main central segment towards the nw are associated to surface folding therefore the total length of the fault and fold zone is about 40 km in agreement with the rupture length and seismic moment obtained on the basis of surface wave modelling well developed uplifted terraces in the northern block and subsiding valleys in the southern block indicate past quaternary activity in the fault region palaeoseismological evidence of ancient earthquakes has been recognized in trenches across the spitak fault one old event occurred between 17 000 years bp and the beginning of the formation of present day soil

fault location and rupture kinematics of the magnitude 6 8 1992 erzincan earthquake turkey from strong ground motion and regional records abstract the hypocenter location of the 13 march 1992 m 6 9 erzincan earthquake turkey and its rupture kinematics have been studied using local and regional seismic records to understand its relationship with the tectonic activity of the erzincan basin and of the north anatolian fault naf regional records of the mainshock and the largest aftershocks were used to locate the respective epicenters the mainshock s p travel time delay and the p wave polarization of the near source accelerogram record in erzincan erz calibrated by the aftershock records constrain the mainshock hypocenter to be located about 10 km to the east southeast of erzincan 39 42 3 n 39 35 2 e and at a best fit depth of about 9 km the activated fault is a major branch of the naf along the eastern edge of the basin hypocentral depths greater than about 16 km are not supported by the data the ground velocity record at erz has been synthesized for constraining the northwestward rupture assuming a kinematic model with constant slip and rupture velocity and a strike 125 for a large number of models the latter were constructed by varying the rupture parameters in a discrete domain the best fit fault models are located within 1 km of the epicenter above and have all their northwestern end within 5 km of erz the up dip limit of the rupture in the vicinity of erz ranges from 5 to 2 km in depth in agreement with the absence of surface breakage the estimated rupture velocity is 3 km sec the rise time is 0 35 sec and the mean slip of about 1 m is poorly resolved with a standard uncertainty of 0 5 m being strongly sensitive to the rupture velocity and to the fault location combining these results with the seismic moment and the source duration provided by other studies leads to a total rupture length ranging between 20 and 35 km the rupture thus propagated bilaterally on the naf and was confined within the limits of the basin stopping to the southeast near the intersection of the naf with the ovacik fault

the dynamics of the 2001 etna eruption as seen by full moment tensor analysis summary the mt etna eruption of july 2001 was announced by severe seismic activity and by the opening of a 7 km long zone of densely distributed fractures the large amount of data collected gave a unique opportunity to study the magma migration process and to infer the position and geometry of the uprising dyke results from multidisciplinary approaches suggest that the observed phenomenology was the result of the rapid intrusion of a vertical dyke oriented roughly n s and located a few km south of the summit region to add new constraints to the dynamics of the eruption process in this study we determine the full seismic moment tensors of 61 earthquakes selected among those occurring between july 12 and july 18 md 2 2 located in a depth ranging from 1 km above sea level a s l to 3 km below sea level b s l at the beginning of the seismic swarm the dominant component of the seismic source tensor is double couple percentage around 65 per cent on average statistical significant at 95 per cent confidence level and in the following hours the non double couple components increase at the expenses of the double couple such observations are related well with the system of fractures formed just before the eruption whereas the increasing non double couple components can be explained as the response of the confining rocks to the rising magma and degassing processes the type of focal mechanisms retrieved are predominantly of normal fault type 44 per cent strike slip 30 per cent and thrust mechanisms 9 per cent and outline a scenario that concurs with the stress regime induced by a dyke injection the space time analysis of seismic source locations and source moment tensors 1 confirms the evidence of a vertical dyke emplacement that fed the 2001 lateral eruption and 2 adds new insights to support the hypothesis of the injection of a second aborted dyke 2 km se from the fractures zone

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

late cenozoic tectonism and landscape development in the foreland of the andes northern sierras pampeanas 26 28 s argentina the argentine sierras pampeanas are reverse fault bounded mountain blocks of precambrian to paleozoic basement rocks in the foreland of the central andes uplift in the northernmost sierras pampeanas fault blocks of sierra de quilmes sierra cumbres calchaquies and sierra aconquija started about 7 ma and became pronounced between 4 and 3 4 ma the movements culminated after 2 9 ma when the conformable mio pliocene santa maria group was overthrusted faulted and folded in the course of principal basement uplift these movements created climate and base level conditions that resulted in the formation of five pediment levels in the deformed basin strata between 2 5 and 0 3 ma tectonically induced base level changes in the piedmont resulted in three tectonism related pediment surfaces between 2 5 and 0 6 ma which attest to the neotectonic activity in the andean foreland the chronology of young tectonic uplift contradicts models in which early uplift between 20 and 13 ma is due to the interaction between high topography on the subducting nazca plate and the south american craton in conjunction with the principal uplift of the adjacent puna plateau the northernmost sierras pampeanas are better explained by e w compressional stresses superposed on a thinned lithosphere and inherited zones of structural weakness that facilitated uplift

lithospheric flexural strength and effective elastic thicknesses of the eastern anatolia turkey and surrounding region abstract the lithospheric structure of eastern anatolia and the surrounding region including the northern part of the arabian platform is investigated via the analysis and modeling of bouguer anomalies from the earth gravitational model egm08 the effective elastic thickness of the lithosphere eet that corresponds to the mechanical cores of the crust and lithospheric mantle is determined from the spectral coherence between bouguer anomalies and surface elevation data its average value is 18 7 km from the logarithmic amplitude spectra of bouguer anomalies average depths of the lithosphere asthenosphere boundary lab moho conrad and basement in the study area are constrained at 84 km 39 km 16 km and 7 km respectively the geometries of the lab and moho are then estimated using the parker oldenburg inversion algorithm we also present a lithospheric strength map obtained from the spatial variations of eet determined by yield stress envelopes yse the eet varies in the range of 12 23 km which is in good agreement with the average value obtained from spectral analysis low eet values are interpreted as resulting from thermal and flexural lithospheric weakening according to the lithospheric strength of the eastern anatolian region the rheology model consists of a strong but brittle upper crust a weak and ductile lower crust and a weak lower part of the lithosphere on the other hand lithosphere strength corresponds to weak and ductile lower crust a strong upper crust and a strong uppermost lithospheric mantle for the northern part of the arabian platform

epicentre accuracy based on seismic network criteria summary we establish reliable and conservative estimates for epicentre location accuracy using data that are readily available in published seismic bulletins a large variety of seismic studies rely on catalogues of event locations making proper assessment of location uncertainty critical event location and uncertainty parameters in most global regional and national earthquake catalogues are obtained from traditional linearized inversion methods using a 1 d earth model to predict traveltimes reported catalogue uncertainties are based on the assumption that error processes are gaussian zero mean and uncorrelated unfortunately these assumptions are commonly violated leading to the underestimation of true location uncertainty especially at high confidence levels we find that catalogue location accuracy is most reliably estimated by station geometry we make use of two explosions with exactly known epicentres to develop local network location 0 2 5 accuracy criteria using monte carlo simulations of network geometry we find that local network locations are accurate to within 5 km with a 95 per cent confidence level when the network meets the following criteria 1 there are 10 or more stations all within 250 km 2 an azimuthal gap of less than 110 3 a secondary azimuthal gap of less than 160 and 4 at least one station within 30 km to derive location accuracy criteria for near regional 2 5 10 regional 2 5 20 and teleseismic 28 91 networks we use a large data set of exceptionally well located earthquakes and nuclear explosions beyond local distances we find that the secondary azimuthal gap is sufficient to constrain epicentre accuracy and location error increases when the secondary azimuthal gap exceeds 120 when station coverage meets the criterion of a secondary azimuth gap of less than 120 near regional networks provide 20 km accuracy at the 90 per cent confidence level while regional and teleseismic networks provide 25 km accuracy at the 90 per cent confidence level

how flat is tibet high resolution digital topography three arc second grid for most of tibet provides new information to characterize the relief of the highest and largest plateau on earth the arid to semiarid central and northern part of the plateau interior has low relief average slopes of over 250 m windows and a mean elevation of 5023 m above sea level at moderate wavelengths of m relief is or less for most of tibet as opposed to the much higher relief of up to 6 km on the plateau edges where glacial and fluvial dissection is greater because of higher levels of precipitation the only faults manifesting significant topographic relief are the relatively small scale generally north trending graben systems primarily in southern tibet and several large scale fault systems near the edges of tibet the flatness of tibet implies that 1 there has been little deformation especially shortening of the uppermost crust north of the graben systems during the late cenozoic and 2 shallow crustal isostatic compensation has been acting to level the surface of the plateau

shallow structure beneath the central volcanic complex of tenerife from new gravity data implications for its evolution and recent reactivation abstract we present a new local bouguer anomaly map of the central volcanic complex cvc of tenerife spain constructed from the amalgamation of 323 new high precision gravity measurements with existing gravity data from 361 observations the new anomaly map images the high density core of the cvc and the pronounced gravity low centred in the las canadas caldera in greater detail than previously available mathematical construction of a sub surface model from the local anomaly data employing a 3d inversion based on growing the sub surface density distribution via the aggregation of cells enables mapping of the shallow structure beneath the complex giving unprecedented insights into the sub surface architecture we find the resultant density distribution in agreement with geological and other geophysical data the modelled sub surface structure supports a vertical collapse origin of the caldera and maps the headwall of the ca 180 ka icod landslide which appears to lie buried beneath the pico viejo pico teide stratovolcanic complex the results allow us to put into context the recorded ground deformation and gravity changes at the cvc during its reactivation in spring 2004 in relation to its dominant structural building blocks for example the areas undergoing the most significant changes at depth in recent years are underlain by low density material and are aligned along long standing structural entities which have shaped this volcanic ocean island over the past few million years

geodynamics seismicity and seismic hazards of the caucasus abstract being a part of ongoing continental collision between the arabian and eurasian plates the caucasus region is a remarkable site of moderate to strong seismicity where devastating earthquakes caused significant losses of lives and livelihood in this article we survey geology and geodynamics of the caucasus and its surroundings magmatism and heat flow active tectonics and tectonic stresses caused by the collision and shortening gravity and density models and overview recent geodetic studies related to regional movements the tectonic development of the caucasus region in the mesozoic cenozoic times as well as the underlying dynamics controlling its development are complicated processes it is clear that the collision is responsible for a topographic uplift inversion and for the formation of the fold and thrust belts of the greater and lesser caucasus tectonic deformations in the region is influenced by the wedge shaped rigid arabian block indenting into the relatively mobile region and producing near n s compressional stress and seismicity in the caucasus regional seismicity is analysed with an attention to sub crustal seismicity under the northern foothills of the greater caucasus which origin is unclear whether the seismicity associated with a descending oceanic crust or thinned continental crust recent seismic tomography studies are in favour of the detachment of a lithospheric root beneath the lesser and greater caucasus the knowledge of geodynamics seismicity and stress regime in the caucasus region assists in an assessment of seismic hazard and risk we look finally at existing gaps in the current knowledge and identify the problems which may improve our understanding of the regional evolution active tectonics geodynamics shallow and deeper seismicity and surface manifestations of the lithosphere dynamics among the gaps are those related to uncertainties in regional geodynamic and tectonic evolution e g continental collision and associated shortening and exhumation lithosphere structure deformation and strain stress partitioning and to the lack of comprehensive datasets e g regional seismic catalogues seismic gravity and geodetic surveys

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

v s of the uppermost crust structure of the campi flegrei caldera southern italy from ambient noise rayleigh wave analysis abstract shear wave velocities v s are defined in the uppermost 1 2 km of the campi flegrei caldera through the non linear inversion of the group velocity dispersion curves of fundamental mode rayleigh waves extracted from ambient noise cross correlations between two receivers noise recordings three months long at 12 seismic stations are cross correlated between all couples of stations the experiment provided successful results along 54 paths inter stations distance of which 27 sampled a depth 1 km v s contour lines are drawn from 0 06 km b s l to 1 km depth b s l and show difference between the offshore gulf of pozzuoli and coastline and the onshore areas at 0 06 km b s l the gulf of pozzuoli and the coastline are characterized by v s of 0 3 0 5 km s and of 0 5 0 7 km s respectively such velocities are typical of neapolitan pyroclastic soils and fractured or altered tuffs the inland shows v s in the range 0 7 0 9 km s typical of neapolitan compact tuffs velocities increase with depth and at 1 km depth b s l velocities lower than 1 5 km s are still present in the gulf and along the coastline while velocities higher than 1 9 km s characterize the eastern sector grossly coincident with the neapolitan yellow tuff caldera rim the s vito plain and the area between solfatara and sw of astroni such features are much more evident along two cross sections drawn in the offshore and onshore sectors by integrating our v s models with literature data our models join previous noise cross correlation studies at greater scale at depths of 0 7 0 8 km hence the picture of the campi flegrei caldera is shown up to a depth of 15 km v s of about 1 7 km s corresponding to compression velocities v p of about 3 km s computed by using the v p v s ratio resulted in the inversion are found at depths of 1 1 km in the centre of the gulf of pozzuoli and at a depth of about 0 7 km b s l onshore an increment of v s velocity 1 9 2 0 km s is locally observed onshore which might be attributed to a layer of tuffs and tuffites interbedded with thin lava beds according to the correlation of v s with stratigraphies in the deep drillings of s vito

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

seismic versus aseismic deformation in iran inferred from earthquakes and geodetic data summary a combined analysis of the geodetic strain rate field and the strain rate field deduced from the seismicity allows us to define the style of deformation and to distinguish seismic from aseismic deformation we perform this analysis in iran where the present day tectonics results from the north south convergence between the plates of arabia to the south and eurasia to the north the data consist of velocities measured with a gps network of 28 benchmarks and of instrumental and historical earthquake catalogues the axes of the seismic strain rate tensor have similar orientations to those deduced from the gps velocity field this indicates that the seismicity can be used to improve gps information on the style and the orientation of the deformation comparison of seismic and geodetic strain rates indicates that highly strained zones experience mainly aseismic deformation in southern iran and seismic deformation in northern iran a large contrast is observed between the zagros less than 5 per cent seismic deformation and the alborz kopet dag regions more than 30 100 per cent seismic deformation the distribution of the seismic geodetic ratio correlates with the distribution of large earthquakes intensive low magnitude seismicity is observed in the zagros whereas the largest earthquakes occur in northern iran the contrast of seismic deformation between the zagros and peri caspian mountains is confirmed considering 300 or 1000 yr of seismicity rather than 100 or 200 yr

rate of active shortening across the southern thrust front of the greater caucasus in western georgia from kinematic modeling of folded river terraces above a listric thrust abstract although the greater caucasus gc mountains accommodate a significant fraction of orogen perpendicular arabia eurasia convergence at their longitude the locations and slip rates of the active structures absorbing this shortening are poorly known here we report the first late quaternary shortening rate for an active thrust in the gc determined from dating and reconstructing a deformed landform in the rioni basin along the southwestern flank of the gc terraces along the enguri river have been folded by the south vergent tsaishi anticline and record quaternary shortening along the southernmost exposed frontal structure terrace surfaces are well preserved and together with underlying mesozoic to neogene strata clearly record folding we use high resolution topographic data from differential gps surveys and bedding attitudes across the fold to construct a kinematic model that describes both the terrace deformation and finite shortening across the anticline recorded by the folded strata we calculate that a deformed terrace records 106 1 38 7 36 4 m of slip since abandonment optically stimulated luminescence dating of quartz in a loess cap on this terrace indicates it was abandoned before 94 1 12 8 ka implying a geologic shortening rate of 1 09 0 62 0 43 mm yr since 100 ka this work confirms that the frontal structure of the rioni fold thrust belt is quaternary active but has a rate that falls short of the regional geodetic shortening rate of 3 5 mm yr we infer that the missing late quaternary shortening is accommodated by additional structures within the gc to the north folding of late quaternary terraces and a possible coseismic scarp along the frontal structure of the gc together imply that structures in the western gc may be capable of coseismic rupture within and beneath the adjacent basin in addition to blind ruptures within the main range such as the 1991 racha earthquake thus the gc system appears to be broadly analogous to the himalaya where the foreland fold thrust belt connects by a shallow seismogenic detachment to structures beneath the main range the geometry of this detachment may influence earthquake rupture initiation and propagation potentially playing a significant role in the seismic hazard of the gc

erosion and tectonics at the margins of continental plateaus the topography across the eastern margin of the central andean plateau north of 18 s beni region bears a strong resemblance to the topography of the southern margin of the tibetan plateau nepal himalaya with both regions featuring a steep frontal slope and high peaks at the plateau edge in contrast the topography of the eastern margin of the central andean plateau south of 18 s pilcomayo region tapers toward the foreland more gently and has no line of high peaks at the margin both the himalayan and the beni regions have been the sites for large amounts of denudation and in both regions geologic evidence suggests that erosion has been sufficiently vigorous for the physiographic plateau margin to have retreated toward the plateau interior during the neogene we hypothesize that the steep frontal slope and high peaks of the beni region and himalayan front largely reflect the high orographic precipitation and high erosion rates occurring in these regions and that the more gentle topography of the semiarid pilcomayo region reflects a tectonic landform only slightly modified by erosion we propose that orographic precipitation impinging on a plateau margin will generally tend to drop moisture low on the slope eroding back the plateau while enhancing or maintaining the steep long wavelength slope a numerical model coupling orographic precipitation erosion and tectonic uplift demonstrates the plausibility of this hypothesis the erosional efflux in both the beni and nepal himalaya have been considerable and simple mass balance calculations for the himalaya suggest that during the neogene the erosional mass efflux has generally outpaced the tectonic mass influx this contrasts with the apparent prior domination of tectonic influx and may reflect a decrease in the rate of tectonic addition during the same period and or increased late cenozoic erosion rates

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

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

average pleistocene climatic patterns in the southern central andes controls on mountain glaciation and paleoclimate implications abstract despite elevations of 5000 6800 m modern glaciers occur along the southern puna plateau and the northern sierras pampeanas in the southern central andes the modern snowline rises from 5100 m in sierra aconquija to 5800 m in the puna as a result of a westward decrease in precipitation from 450 to less than 100 mm yr during the pleistocene these arid highlands experienced multiple cirque and valley glaciation that likely postdate the last interglacial period although lack of age control prevents an absolute chronology glaciation in the puna and along the eastern puna edge produced a 300 m pleistocene snowline psl depression while in the sierras pampeanas the psl depression was at least 900 m the greater psl depression in the sierras pampeanas is best explained by a combination of cooling and increase of easterly moisture whereas the psl depression in the puna appears more sensitive to moisture increases than temperature previously glaciations in this region have been explained by increa

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

seismic site amplification factors in campi flegrei southern italy the method of spectral ratios of s waves from local small earthquakes recorded at various sites in the campi flegrei volcanic area southern italy has been used to evaluate the seismic site response in the frequency range 1 15 hz the spectra of the s wave trains recorded at the short period seismic stations are corrected for attenuation using attenuation parameters quality factor q previously determined for the area using the coda method a reference station has been used selected on the basis of the highest number of recorded earthquakes and not on geological considerations the relative uniformity of the geological conditions and the absence of hard rock sites conditioned such choice the method has been checked using the coda wave method to estimate the spectral site response and similar results were obtained the results show a relative peak of the spectral ratio pattern centred at low frequency 2 3 hz and a minimum of 0 2 at 8 hz for two stations located on yellow tuff such results are interpreted as being caused by a filtering effect produced by selective attenuation such a pattern could be of interest for seismic engineering purposes in view of the abundance of tuff over a wide area in this densely inhabited region

deep structures along the boundary of a collisional belt attenuation tomography of p and s waves in the greater caucasus summary seismic attenuation q 1 o fp and s waves shows a major discontinuity from the russian platform to the tectonically active greater caucasus broadband records show this boundary over paths 4 long as revealed by the decay of amplitude spectra from a digital seismic network flanking the greater caucasus we measure attenuation from individual spectra using a non linear least squares procedure to determine an attenuation parameter t simultaneously with source parameters at frequencies between 1 and 15 hz the t measurements are then inverted for spatial variations of q 1 with parametrizations of varying complexity model variance for heterogeneous structures improves by more than 30 per cent compared with homogeneous parametrizations site corrections also significantly improve the fit in these inversion results mountainous regions exhibit q values 2 3 times lower q s 775 75 than do the adjacent shields q s 2060 315 showing that the discontinuity is large for both regions q p is roughly equal to q s comparison of body wave to coda spectra indicates that intrinsic absorption rather than scattering dominates the q 1 measurements at least beneath the mountains hence q 1 variations may give a reasonable proxy for temperature if so then temperature beneath the mountains exceeds that beneath the shield by 70 400 c these temperature increases may not be high enough to generate widespread partial melting beneath the mountains but could produce regional metamorphism and could contribute substantially to isostatic compensation of the mountains whatever their origin the boundary in seismic attenuation is abrupt and large between stable craton and an adjacent mountain belt demonstrating that q 1 is a sensitive indicator of tectonic process

an analysis of the 1985 nahanni earthquakes abstract two large magnitude earthquakes occurred in 1985 near the north nahanni river in the northeast cordillera northwest territories canada on 5 october m s 6 6 and 23 december m s 6 9 these events were unprecedented for this region of the cordillera and the december event is the largest earthquake ever known in the eastern part of the canadian cordillera this report presents detailed studies of the nahanni earthquakes their source parameters macroseismic effects aftershock sequences triggered rock avalanches their relationship to the geology of the epicentral area and their seismic hazard implications parameters calculated here for these two major events are parentheses indicate other studies the earthquakes occurred within a small relatively undeformed plateau the mackenzie plain in the foreland fold belt created along the northeastern cordillera during the columbian or laramide orogeny that fold belt is now subjected to northeast southwest horizontal compressive stresses possibly very similar to the original laramide stress regime and the fault plane implied by the seismic mechanisms is very similar to the laramide faults in the area however no surface fault break has been found and none of the mapped laramide faults in the epicentral area appears to be involved in the aftershock activity it is thus believed that the nahanni earthquakes occurred on a blind laramide thrust fault under the mackenzie plain the large magnitudes of the nahanni earthquakes show that the present seismic zoning for building code purposes in the eastern cordillera north of 60 n needs reassessment and suggest that the zoning in the eastern cordillera in british columbia and alberta may also need revision the felt areas of the earthquakes show that regional anelastic attenuation in the eastern canadian cordillera is significantly anisotropic and much lower along strike than across strike the felt areas also appear to scale with seismic moment rather than m b magnitude the thrust mechanisms regional stress regime shallow focal depth and high velocity sedimentary rocks in the focal region suggest that the nahanni earthquakes and particularly the near field strong ground motion recorded for the second event are ideal engineering design data for critical facilities in eastern north america

active convergence between the lesser and greater caucasus in georgia constraints on the tectonic evolution of the lesser greater caucasus continental collision abstract we present and interpret newly determined site motions derived from gps observations made from 2008 through 2016 in the republic of georgia which constrain the rate and locus of active shortening in the lesser greater caucasus continental collision zone observation sites are located along two 160 km long profiles crossing the lesser greater caucasus boundary zone one crossing the rioni basin in western georgia and the other crossing further east near the longitude of tbilisi convergence across the rioni basin profile occurs along the southern margin of the greater caucasus near the surface trace of the north dipping main caucasus thrust fault mctf system and is consistent with strain accumulation on the fault that generated the 1991 m w 6 9 racha earthquake in contrast convergence along the tbilisi profile occurs near tbilisi and the northern boundary of the lesser caucasus near the south dipping lesser caucasus thrust fault approximately 50 70 km south of the mctf which is inactive within the resolution of geodetic observations 0 5 mm yr at the location of the tbilisi profile we suggest that the southward offset of convergence along strike of the range is related to the incipient collision of the lesser greater caucasus and closing of the intervening kura basin which is most advanced along this segment of the collision zone the identification of active shortening near tbilisi requires a reevaluation of seismic hazards in this area

the caucasus an actual example of the initial stages of continental collision abstract a field study of the neotectonics of the georgian caucasus is combined with geophysical geodetic and geological information in order to obtain a mechanical model of actual deformation the analysis of satellite photos together with topographical and geological maps shows that the great caucasus is bisected by a nne trending sinistral strike slip fault zone the western great caucasus is thrusted to the south over the rioni basin while on the other hand its northern flank is a monocline that descends gently into the russian platform active volcanism is present from elbruz to kazbeg the eastern great caucasus is limited by thrusts to the north and to the south and intermediate structures are disposed in a fan like shape no recent volcanism is observed the eastern limit of the chain is a nnw trending dextral strike slip fault zone seismicity from a local network illustrates the activity of the thrusts and gives evidence for the strike slip faults microtectonic data confirm the recent activity and the sinistral character of the borjomi kazbeg strike slip fault the strike slip faults bordering the eastern caucasus may be seen as the limits of a plastic wedge in front of the arabian plate at an early stage of continental collision

active stress field and fault kinematics of the greater caucasus abstract this work contributes to depict the current seismicity fault kinematics and state of stress in the greater caucasus territories of georgia azerbaijan and russia we merged and homogenized data from different earthquake catalogues relocated 1000 seismic events created a database of 366 selected focal mechanism solutions 239 of which are new and performed a formal stress inversion preferential alignments of crustal earthquake foci indicate that most seismic areas are located along the southern margin of the belt and in the north eastern sector this is consistent with the presence of dominant active wnw ese faults parallel to the mountain range in the entire greater caucasus a dominant nne ssw oriented greatest principal stress 1 controls the over all occurrence of earthquakes of minor and major magnitude main earthquakes are characterized by a vertical least principal stress 3 corresponding to reverse kinematics reverse slip is more common along the southwestern and north eastern foothills of the greater caucasus although in these areas there are also scattered strike slip events this suggests the presence of local stress fields with horizontal 1 and 3 in the central southern part of the mountain belt in correspondence of the local collision between the lesser and the greater caucasus 1 rotates to nnw sse the strike slip events instead dominate along the southern flank of the central eastern mountain range this is interpreted as the effect of the collision that promotes eastward escape of the tectonic blocks located to the east

active tectonics of central western caucasus georgia abstract this work contributes to a better knowledge of potentially seismogenic faults of the georgia greater and lesser caucasus by evaluating the distribution of earthquake foci active tectonic stress field kinematics and geometry of main fault planes we consider all the information coming from field structural geology geomorphology seismological data from historical and instrumental catalogues seismic reflection sections as well as new focal mechanism solutions these data enable recognizing some active ene wsw reverse faults in the core of the greater caucasus that are parallel to the mountain range at the southernmost front of the greater caucasus a series of main thrusts dipping towards nne are active with up to hundreds km long segments along this thrust zone a potentially locked segment is present about 90 km long the studied section of the lesser caucasus has active structures along the northern front given by south dipping thrusts as well as in the central core where strike slip and oblique faults coexist the transcaucasian depression between the two mountain ranges shows an ongoing inversion tectonics of the central part of the rioni basin where active n to ne dipping reverse faults are present accompanied by clear evidence of uplift of a wide area the data are coherent with a n s to nne ssw contraction of the central western greater caucasus and lesser caucasus although in general the seismicity decreases westward in terms of number of earthquakes and magnitude seismological and geological structural data in the rioni basin indicate here a quaternary propagation of deformation towards the west

the spitak armenia earthquake of 7 december 1988 field observations seismology and tectonics the epicentre of the destructive earthquake that devastated northern armenia the strongest in the region since historical times is located within the lesser caucasus a mountain country subjected to north south compression by the push of the arabian plate a french soviet field expedition studied surface breaks and aftershock activity the fault scarp could be followed for 13 kilometres and showed a reverse dislocation of 1 6 metres aftershocks are shallower than 13 kilometres and delimit a ruptured surface of about 300km2

postseismic deformation following the 1991 racha georgia earthquake 1 the 1991 ms 7 0 racha earthquake is the largest ever recorded in the caucasus mountains approximately three months after this thrust faulting earthquake a gps network was set up to measure postseismic surface deformation we present an analysis of these data which indicate accelerated postseismic motions at several near field sites we model this deformation as either afterslip on the rupture surface or viscoelastic relaxation of the lower crust we find that the postseismic motions are best explained by shallow afterslip on the earthquake rupture plane the minimum postseismic moment release is estimated at 6 0 1018 n m which is over 200 times the moment released by aftershocks in this same period and about 20 of the coseismic moment we also show that the effective viscosity of the lower crust in the western greater caucasus region exceeds 1018 pa s

the rupture process of the armenian earthquake from broad band teleseismic body wave records summary the destructive earthquake of december 1988 in armenia m 6 9 was recorded on broad band and very long period channels at teleseismic distances by geoscope and gdsn networks these records are well distributed in azimuth and allow a detailed study of the rupture process of this earthquake the average focal mechanism obtained by p and sh wave modelling c i 300 f lo 6 63 f 5 a 100 f 20 is compatible with the mechanism obtained from very long period surface waves and intermediate period single station determinations as well as field observations the mean depth of the rupture is also fixed by waveform modelling between 5 and 7 km which means that the rupture surface extends from the surface to a depth between 10 and 14 km in agreement with aftershock depth distribution the rupture is found to be complex composed of a weak beginning or a small foreshock and two pulses well separated in time the time delay between the two events is estimated for each station by waveform modelling and by spectral analysis the azimuthal variation of this time delay is interpreted in terms of direction and velocity of rupture on the fault plane a more detailed analysis of the source implies the use of additional information coming from aftershock studies and tectonics we use forward modelling to investigate several rupture mechanisms a three source model gives an acceptable fit to the observed records but the western mechanism is at odds with observed tectonics and furthermore rupture propagation is not well simulated a five segment model of the source obtained from field seismotectonic data gives a better waveform fit a time sequence of individual breaks that simulates a rupture propagating away from the hypocentre and subsource mechanisms that are compatible with surface tectonics

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

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

determination of the seismic moment tensor for local events in the south shetland islands and bransfield strait we present the results of the analysis for a set of earthquakes recorded in the bransfield strait and the south shetland islands in the period 1997 1998 to determine focal mechanisms and source time functions events with magnitudes between 3 and 5 6 have been analysed and the source parameters have been retrieved using a robust methodology inpar that allows the reliable inversion of a limited number of noisy records this methodology is particularly important in oceanic environments where the presence of seismic noise and the small number of stations makes it difficult to analyse small magnitude events

geometry segmentation and stress regime of the spitak armenia earthquake from the analysis of the aftershock sequence summary the aftershock sequence of the spitak earthquake as recorded by a dense portable network deployed around the source region is analysed in order to obtain a precise description of the mechanics of the rupture a collection of 708 well recorded events corresponding to a period of about two weeks is studied their hypocentres are accurately located and their focal mechanisms are calculated individually as well as by a joint procedure that permits us to estimate the stress regime the epicentral distribution of these aftershocks indicates that the fault at depth extends well beyond the surface rupture towards the west and northwest neotectonic and seismic observations permit us to identify five segments broken during the earthquake the southeastern one oriented n140 corresponds to the surface ruptures along the alavar right lateral shear fault the main surface ruptures between spitak and gekhasar correlate well with aftershocks showing a n120 trending fault surface dipping 50 to the ne and acting as a thrust with a right lateral component two similar segments towards the west are offset and hidden under active folds a fifth segment towards the nw corresponds to a right lateral blind shear fault buried in depth in the vicinity of the large pambak sevan fault 14 vertical sections across the fault including focal mechanisms illustrate these features a relocation of the main shock and aftershocks for the period before the installation of the portable network confirms the spatial extent of the seismicity the foreshock the main shock and the strongest aftershock 4min 20s after the main shock have approximately the same epicentre thus the rupture started at the crossing of the pambak sevan and alavar faults and propagated bilateraly from there although the seismic moment associated to the alavar branch is only about one sixth of the total moment the stress regime is one of triaxial compression with a a axis oriented n344 the same orientation is given by the microtectonic observations made on the central segment of the surface ruptures a result that agrees with previous estimates for the georgian caucasus

dip range for intracontinental reverse fault ruptures truth not stranger than friction abstract histograms of fault dips have been compiled for moderate to large m 5 5 reverse slip intracontinental earthquakes with the slip vector raking 90 30 in the fault plane the principal data set is restricted to earthquakes where the fault plane in the focal mechanism can be unambiguously distinguished from the auxilliary plane the reverse fault dips are bracketed within the range 12 1 the observed dip range is consistent with reactivation of faults possessing rock friction coefficients within byerlee9s 1978 range 0 85 s 0 6 undergoing frictional lockup at dips approaching 60 the broad 25 to 35 peak may arise from progressive domino steepening of imbricate reverse faults above the optimal dip for reactivation in regions undergoing bulk shortening paucity of very low angle thrusts implies that it is generally the steeper ramps within ramp flat assemblages that fail in moderate to large earthquakes the subsidiary peak at 45 to 55 likely results from compressional reactivation of former normal faults in areas undergoing tectonic inversion requiring some degree of fluid overpressuring the results are consistent with previous studies on the dip range for active normal faults that again demonstrate frictional lockup at reactivation angles approaching 60 together these analyses suggest that byerlee friction coefficients apply to faults with displacements of up to a few kilometers

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

geodynamic evolution of the caucasus and adjacent areas in alpine time abstract the alpine geodynamics of the caucasus and adjacent areas is discussed palinspastic reconstructions are given on the basis of new geologic paleomagnetic and paleobiogeographic data the dynamic unity of extension and compression processes is shown to take place within the central segment of the mediterranean belt the closure of the paleotethys oceanic basin coincides approximately with the opening of the mesotethys owing to this the opening between afro arabia and eurasia persists as is confirmed by paleomagnetic and other data the closure of the mesozoic tethys is on the whole synchronous with the opening of the central and south atlantic the formation of the present structure of the caucasus and adjacent areas is connected with the unidirectional compression of this area and the rotation of the compressional axis from a northeastern to a sub meridional direction in the course of the cimmerian alpine cycle

stress tensor and fault plane solutions for a population of earthquakes an algorithm for the simultaneous estimation of the orientation and shape of the stress tensor and the individual fault plane solutions for a population of earthquakes is studied it corresponds to a synthesis of the methods used by brillinger et al 1980 to obtain focal mechanisms and by armijo and cisternas 1978 for stress tensor analysis in microtectonics the input data are the polarities of the p arrival and take off angles for the set of source station pairs the method distinguishes in general which one of the nodal planes corresponds to the fault and gives the direction of the slip the application to the aftershock sequence of the 1980 arudy earthquake western pyrenees shows that the observations may be explained by a single stress tensor producing a n32 e extension with a likelihood of 95 per cent

monitoring volcanic and geothermal areas by full seismic moment tensor inversion are non double couple components always artefacts of modelling non double couple mechanisms ndc in volcanic environments are good indicators of local modifications of stress induced by dike injection high fluid pressure movements or by thermal cooling nevertheless the possible biasing effects of wave propagation in structurally complicated regions the presence of noise or a not appropriate station coverage can make the identification of ndc as true source phenomena uncertain in this paper we illustrate possible sources of fake ndc and we demonstrate that by the error analysis that we apply it is possible to discriminate spurious artifacts and physically meaningful solutions tests with synthetic seismograms and the analysis of observed ones in volcanic and geothermal areas are thoroughly discussed

improving sparse network seismic location with bayesian kriging and teleseismically constrained calibration events monitoring the comprehensive nuclear test ban treaty will require improved seismic location capability for small magnitude events the international monitoring system ims is well suited to locate events that are large enough to be recorded at teleseismic distances however small events are likely to be recorded on a sparse subset of ims stations at regional to upper mantle distances less than 30 and sparse network locations can be strongly effected by travel time errors that result from path specific velocity model inaccuracies in an effort to improve sparse network location capability we outline a procedure that applies empirical corrections to travel times determined with an appropriate velocity model more specifically bayesian kriging and calibration events constrained with a global network are used to estimate epicenter specific travel time corrections for a test sparse network of stations we calculate travel time residuals for the calibration events relative to the ak135 velocity model travel time residuals are assigned to the respective calibration epicenter forming a set of spatially varying travel time correction points the spatial set of correction points is declustered to reduce the dimension of the observations with minimal reduction in accuracy of the travel time corrections we then use the declustered set of calibration points and bayesian kriging to form continuous travel time correction surfaces for each station of the test network the effectiveness of travel time correction surfaces is evaluated by locating with and without corrections a subset of the 1991 racha earthquake sequence caucasus mountains for which we have accurate locations that were independently determined with a dense local network when no travel time correction is applied the mean horizontal distance between the local and test network locations is 42 km and there is a distinct bias in sparse network locations toward the north northwest the mean difference between local and sparse network locations is cut to 13 km when corrections are applied and the bias in location is significantly reduced when calibration events in the racha vicinity are not used to make the correction surfaces there is still a significant improvement in location with mean mislocations of 15 km when corrections are not applied only one of the locally determined locations lies within the associated 90 coverage ellipse determined with the test sparse network however by using travel time corrections and estimates of model uncertainty determined using kriging representative error ellipses are obtained this study demonstrates that kriging correction surfaces based on global network constrained calibration events can improve the ability to accurately locate lower magnitude events while providing representative coverage ellipses

active tectonics of the turkish iranian plateau 1 this paper examines how active faulting in the turkey iran caucasus region accommodates the arabia eurasia collision and the velocity field observed by gps the overall shortening across the zone is in general spatially separated partitioned into right lateral strike slip in the turkish iranian plateau and thrusting in the greater caucasus a band of counterclockwise rotating nw se right lateral strike slip faults accommodates a nw se gradient in ne directed velocity relative to eurasia between the black and caspian seas a nnw sse band of previously unrecognized oblique normal faults is present on the turkey iran border we estimate the offsets on faults from geomorphological features and show that these offsets can be achieved in 5 2 ma at present rates this implies a reorganization of deformation in the collision zone at that time after the initial collision at 12 ma probably in response to mantle induced dynamic uplift

determination of shear and compressional wave velocity variations and hypocenter locations in a rapidly inflating caldera the campi flegrei during 1982 1985 the campi flegrei caldera underwent a large h 1 7 m rapid hmax 2 mm day 1 and localized radius 6 km uplift p and s arrival times from three component digital seismograms recorded during this period have been used to invert for hypocenter locations and for three dimensional shear and compressional velocity to 3 km first order residual based tomography shows a significant and well resolved high p s ratio anomaly for the volume encompassing the central caldera and the active solfatara crater three dimensional tomographic inversion resolves this central anomaly as a zone of depressed p and s with a high 2 1 p s ratio the three dimensional velocity model and hypocenter distribution are consistent with modeling the central caldera as a zone of nearly water saturated cracks presumably a result of recurrent inflation and deflation in a zone with a shallow water table although the presence of small shallow magma bodies is not precluded

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

active thrust front of the greater caucasus the april 29 1991 racha earthquake sequence and its tectonic implications although fault bounded thrust sheest are common in the geological record seismic evidence for their motion is sparse the april 29 1991 racha earthquake m s 7 0 the largest instrumentally recorded earthquake in the greater caucasus is one of the largest recent earthquakes in continental thrust belts and provides evidence on mechanisms of thrust sheet motion using data from a deployment of program for array seismic studies of the continental lithosphere passcal digital seismographs and various other instrumental we locate 1952 aftershocks occurring between may 7 and june 30 1991 the aftershocks form a zone 70 km long and 10 25 km wide striking e w following the racha ridge at the southern boundary of the greater caucasus thrust system teleseismic body waves are inverted for source parameters of the mainshock and the two largest aftershocks the solutions show thrust faulting with centroid depths of 3 10 km comparable to depths of locally recorded aftershocks 2 12 km the shallow dipping nodal plane the aftershock distribution and surface geology demonstrate that the main event was caused by faulting on a thrust system dipping nne at 20 o 31 o bounding the southern slope of the greater caucasus this fault system thrusts the greater caucasus structures south over the dzhirula basement massif the inferred fault geometry suggests that the active fault is either a detachment between sediments and dzhirula basement or cuts through the basement at shallow depths the 1500 m high racha ridge overlies the aftershock zone and is a likely consequence of repeated similar earthquakes hence the 1991 earthquake sequence shows that the western greater caucasus is accommodating plate convergence at a rate possibly comparable to the eastern greater caucasus a few millimeters per year along strike geological discontinuities above and below the thrust surface correspond to the eastern end of the mainshock rupture area no strong evidence for transfer structures could be found along strike suggesting that differences in collisional style between the western and eastern greater caucasus may reflect differences in mechanical properties rather than differences in convergence rate a june 15 1991 event and its aftershocks southeast of the primary aftershock zone along strike show fault planes and slip vectors rotated 41 o clockwise from the mainshock this rotation is consistent with an along strike change in direction of the thrust front near 44 o e longitude and demonstrates strong local structural or topographic control on slip direction the rotation requires along strike shortening within the greater caucasus thrust system at a rate comparable to the rate of thrusting