evidence for lithospheric detachment in the central andes from local earthquake tomography abstract data from three temporary seismic networks were merged for tomographic inversion although the deployments did not coincide in time spatial overlap was achieved by re occupying existing sites travel times and t operators of about 1600 earthquakes were inverted for 3d models of p p s and p wave attenuation q p 1 all three attributes provide a consistent image of the entire subduction zone on a lithospheric scale the tomographic images reveal low velocities and high attenuation in the crust and mantle underlying the western cordillera and most of the puna plateau indicative of weak rheology and mostly asthenospheric mantle in contrast forearc and eastern foreland are characterized by high q p values corresponding to cold temperatures in accordance with thermal models in the backarc between 23 s and 24 s a high velocity high q p structure beneath the eastern cordillera and eastern puna is interpreted as detaching continental lithosphere that has been thickened in the orogenic process south of this structure the mantle is characterized by low velocities high p s ratios and low q p values here it is believed that lithosphere originally underlying andean crust has already been removed this is supported by new estimates of crustal thickness and volcanic activity

receiver function images from the moho and the slab beneath the altiplano and puna plateaus in the central andes summary teleseismic data recorded during one and a half years are investigated with the receiver function technique to determine the crustal and upper mantle structures underneath the highly elevated altiplano and puna plateaus in the central andes a series of converting interfaces are determined along two profiles at 21 s and 25 5 s respectively with a station spacing of approximately 10 km the data provide the highest resolution gained from a passive project in this area so far the oceanic nazca plate is detected down to 120 km beneath the altiplano whereas beneath the puna the slab can unexpectedly be traced down to 200 km depth at longer periods a shallow crustal low velocity zone is determined beneath both plateaus exhibiting segmentation in the case of the altiplano the segments present vertical offsets and are separated by inclined interfaces which coincide with major fault systems at the surface an average depth to moho of about 70 km is determined for the altiplano plateau a strong negative velocity anomaly located directly below the moho along with local crustal thinning is interpreted beneath the volcanic arc of the altiplano plateau between 67 w and 68 5 w a deep section of the puna profile reveals thinning of the mantle transition zone although poorly resolved the detected anomaly may suggest the presence of a mantle plume which may constitute the origin of the anomalous temperatures at the depth of the upper mantle discontinuities

attenuation of high frequency seismic waves beneath the central andean plateau observed patterns of high frequency seismic wave attenuation suggest that near 22 s the upper mantle structure beneath the central andean plateau changes along strike to the south contrasting regions of high and low upper mantle seismic wave attenuation beneath the plateau are identified based on striking azimuthal variations in the character and frequency content of p and s waves propagating beneath the plateau to a portable seismic network deployed in jujuy province argentina 24 s 65 w ray paths from intermediate depth earthquakes located north and northwest of the network transmit seismic waves with a higher frequency content than ray paths from earthquakes at similar depths and distances but located west and south of the network the estimated apparent q values fall into two categories qp 500 and qs 350 for the high q paths and qp 350 and qs 200 for the low q paths in addition sn phases from regional crustal earthquakes in the subandean foreland fold thrust belt to the north propagate efficiently to the jujuy network while sn is not observed from foreland earthquakes located at similar distances to the south of the network these observations combined with data from previously reported wave propagation studies suggest that south of about 22 s the upper mantle beneath the plateau and its adjacent foreland thrust belt is more highly attenuating than the upper mantle farther north forward modeling of the q measurements made at jujuy indicates that the observations can be explained either by a variable thickness high q upper plate beneath the plateau or by a thin variable width very low q zone in the asthenospheric wedge above the subducted slab this lateral variation in upper mantle structure coincides with two physiographically distinct segments of the central andean plateau and its adjacent foreland thrust belt to the east the bolivian altiplano and subandean ranges in the north and the argentine puna and santa barbara system in the south we interpret the north south change in upper mantle attenuation and the corresponding changes in physiography topography and tectonic style at the surface to be due to a mantle lid that is thicker beneath the altiplano and the subandean belt than beneath the puna and the santa barbara ranges

regional variation of morphology of organized convection in the tropics and subtropics 1 properties of organized convection with large horizontal area 1000 km2 and with different horizontal structures in the tropics and subtropics are investigated by using 14 years of tropical rainfall measuring mission observations first the convective features cfs are defined as contiguous areas of convective precipitation detected by the tropical rainfall measuring mission precipitation radar using the minor and major axes of fitted ellipses the morphology of the cfs are described as closer to a circular or a line shape regional variations and the properties of organized convection are examined with cfs with area 1000 km2 after categorizing them by their shapes organized convection tends to have larger extent and a higher fraction of near circular shapes over land than over ocean shallow organized convection with maximum radar echo top height below 4 5 km is found mainly over ocean and some coastal regions of all tropical oceans most shallow organized convection is found over the east pacific the fraction of line shaped organized convection is higher over the ocean than over land and is higher in the subtropics than in the tropics more convective lines are found in winter than in summer over oceans but more in summer over land organized convective lines are slightly less convectively intense indicated by lower 30 dbz echo top heights and warmer 37 ghz brightness temperatures than those with near circular shapes orientations of organized convective lines are often aligned with fronts dry lines warm ocean currents coastlines and mountain slopes over the subtropics organized convective lines are tilted more east west over land and more north south over oceans the largest and the most intense convective lines are found over central africa argentina and southeast u s over land and over several warm currents in subtropical oceans

reply to comment on kinematic variations across eastern cordillera at 24 s central andes tectonic and magmatic implications abstract we discuss in detail all the comments made by petrinovic et al showing that these are not pertinent to the aim of our study or based on incomplete information of fault kinematics or unsupported despite our limited amount of data not any of the raised arguments can be seriously taken into account to alter the proposed scenario therefore we demonstrate that our paper is neither largely speculative nor contains major flaws in particular the limited evidence of pre miocene deformation on a part of a proto eastern cordillera does not affect our interpretation in fact our aim was not to reconstruct the tectonic history of eastern cordillera identifying any pre miocene episode rather it was to define the kinematics of the largest structures affecting its recent evolution therefore the interesting structures described by petrinovic et al also kinematically poorly constrained cannot give useful insights simply because the aim and time frame of our study are different

p and s velocity images of the lithosphere asthenosphere system in the central andes from local source tomographic inversion summary about 50 000 p and s arrival times and 25 000 values of t recorded at seismic arrays operated in the central andes between 20 s and 25 s in the time period from 1994 to 1997 have been used for locating more than 1500 deep and crustal earthquakes and creating 3 d p s velocity and qp models the study volume in the reference model is subdivided into three domains slab continental crust and mantle wedge a starting velocity distribution in each domain is set from a priori information in the crust it is based on the controlled sources seismic studies in slab and mantle wedge it is defined using relations between p and s velocities temperature and composition given by mineral physics each iteration of tomographic inversion consists of the following steps 1 absolute location of sources in 3 d velocity model using p and s arrival times 2 double difference relocation of the sources and 3 simultaneous determination of p and s velocity anomalies p and s station corrections and source parameters by inverting one matrix velocity parameters are computed in a mesh with the density of nodes proportional to the ray density with double sided nodes at the domain boundaries the next iteration is repeated with the updated velocity model and source parameters obtained at the previous step different tests aimed at checking the reliability of the obtained velocity models are presented in addition we present the results of inversion for vp and vp vs parameters which appear to be practically equivalent to vp and vs inversion a separate inversion for qp has been performed using the ray paths and source locations in the final velocity model the resulting vp vs and qp distributions show complicated essentially 3 d structure in the lithosphere and asthenosphere p and s velocities appear to be well correlated suggesting the important role of variations of composition temperature water content and degree of partial melting

lithospheric scale structure across the bolivian andes from tomographic images of velocity and attenuation for p and s waves we have developed a three dimensional lithospheric scale model across the bolivian andes at 20 s based on tomographic images of velocity and attenuation for both p and s waves observations of travel time and attenuation for this study are from regional mantle earthquakes in the subducted nazca plate recorded on a portable broadband seismic array broadband andean joint experiment and seismic exploration of the deep andes in bolivia and chile the shallow mantle under the altiplano from 18 s to 21 s is high velocity and moderately high q vp 8 3 vs 4 7 qp 500 and qs 200 suggesting lithospheric mantle high velocity material in the altiplano extends to a depth of 125 150 km the shallow mantle of the western cordillera is characterized by high vp vs 1 83 suggesting a correlation between vp vs and arc volcanism seismic velocity in the western cordillera mantle is on average only slightly reduced from global averages however velocity and attenuation anomalies are locally strong vp 7 8 vs 4 3 qp 200 and qs 100 consistent with partial melt conditions under the los frailes volcanic field in the eastern cordillera shallow mantle velocity and q decrease drastically from the neighboring altiplano vp 7 8 vs 4 3 qp 300 qs 100 however high vp vs is not as pervasive as it is in the western cordillera we believe that slab derived water and perhaps other volatiles strongly influence the western cordillera while the eastern cordillera low velocity region is more affected by partial melt and or compositional changes average velocity and q in the shallow mantle across the bolivian andes where the tomographic images are best resolved are significantly higher than in most mantle wedge environments where corresponding images are available this is likely the result of a compressional back arc setting in the andes this implies that lithospheric shortening and thickening associated with the formation of the andes has profoundly influenced the shallow mantle structure across the range shallow mantle structure is locally influenced by the subduction processes particularly under the western cordillera however the differing volcanism and seismic character under the two cordilleras suggest that the volcanic process in the eastern cordillera may be distinct from arc volcanism tertiary volcanism in the eastern cordillera is located in the region where mantle shortening is suspected to be greatest both the timing and location of volcanism are consistent with upward migration of mantle wedge asthenosphere following the removal of over thickened lithosphere

observations of mesoscale circulations within extratropical cyclones over the north atlantic ocean during erica abstract pseudo dual doppler analyses of two mesoscale circulations 20 40 km in horizontal dimensions that formed along a warm front within a rapidly deepening extratropical cyclone over the ocean are presented the circulations were analyzed using airborne doppler radar during erica experiment on rapidly intensifying cyclones over the atlantic iop intensive observing period 4 and are believed to be a type of frontal instability that has not been addressed in past theoretical studies of frontal waves and cyclones these features may be the shallow circulations that have been documented to play a role in cyclogenesis when they become coupled with an upper level baroclinic wave the present case is compared and contrasted with the only other well analyzed event during erica iop 5 a retrieval of the perturbation pressure and buoyancy fields using the kinematic wind fields is performed in order to facilitate the interpretation of the dynamic structure of these vortices in addition a set of equations

deep burial of asian continental crust beneath the pamir imaged with local earthquake tomography an inclined zone of intermediate depth seismicity beneath the pamir orogen in central asia has been interpreted as southward subduction of a slab of asian lithosphere however it is not known whether asian lithosphere subducts intact or only partially we used arrival times of shallow and intermediate depth earthquakes recorded with a temporary 2008 2010 seismic network in this region to invert for 3d models of seismic velocities in an attempt to answer this question with local seismicity reaching depths of up to 240 km the deep structure of the pamir could be illuminated with high resolution the resulting velocity models show a north south contrast in crustal seismic velocities in the pamir with very low p velocities 5 7 5 9 km s at 15 30 km depth coupled with relatively low vp vsvp vs 1 70 at mid crustal levels in the southern part of the orogen at sub moho depths we image an arcuate high velocity 8 2 8 6 km s slab dipping south in the eastern pamir and east in the pamir s southwest underlying the intermediate depth earthquakes on top of the high velocity slab and just above the onset of deep seismicity between a depth of 60 to 100 km very low compressional wavespeeds around 7 1 km s and high vp vsvp vs ratios 1 80 attest to subducted crustal rocks additionally we carried out 2d numerical thermomechanical modeling of the continental collision in the pamir focusing on the fate of the crust and mantle lithosphere of the asian and indian plates seismic velocities were computed from the modeling results and the resulting images were compared with the velocity distributions obtained from seismic traveltimes combining tomography and modeling results we infer that a substantial amount of crustal material is pulled down beneath the pamir by cold mantle lithosphere to depths of at least 80 100 km from there on only lower crust and mantle lithosphere continue their subduction and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions the buoyant asian upper and middle crust does not penetrate deeper into the mantle but pools at this depth level from where it might eventually exhume or relaminate

classification of lithology from seismic tomography a case study from the messum igneous complex namibia 1 combined analysis of seismic p and s velocity information provides a reasonable and efficient basis for the petrologic interpretation of seismic cross sections in this paper a methodology is presented which allows extraction of prominent features related to well defined p velocities and poisson s ratios from a tomographic velocity model using a classification approach we used first arrival travel time data from a near vertical seismic experiment and independently determined p and s velocities by forward and inverse modeling resolution and uncertainties were estimated from inverting synthetic data the classification procedure was carried out in two subsequent steps first prominent classes were identified in the parameter space spanned by poisson s ratios and p wave velocities for this purpose a probability density function was calculated from the tomograms a function measuring the topography of the probability density was then determined and a histogram analysis was carried out to detect significant classes in the second step the results from principal component analysis for the identified classes were used to map their distribution along the seismic profile we applied the method to the messum intrusive complex of namibia and identified three prominent classes on the basis of the integration of petrophysical data and comparison with surface geology we conclude that quartz syenite composition dominates the upper 800 m of the crust under the complex outside of the intrusion the upper crust has properties corresponding to felsic metasediments and granites which are abundant in the local basement this material shows strong depth dependent changes of seismic properties which are ascribed to decreasing porosity and fluid saturation with depth

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

p wave attenuation structure in the fault area of the 1995 kobe earthquake the three dimensional 3 d p wave attenuation structure in the kobe epicentral area is determined using aftershock records from the 1995 kobe hyogo ken nanbu earthquake waveform data from both permanent seismic networks and portable stations set up following the kobe mainshock were used the observed p wave amplitude spectra were inverted for the spectral plateau value the source corner frequency and a frequency independent t operator assuming an 2 type source model the calculated t operators were subsequently used for the computation of the 3 d absorption structure using a 3 d velocity model only high quality amplitude spectra were used for the estimation of reliable attenuation parameters resulting in a final data set of 4100 t operators two regions of high absorption were found in the upper part of the crust one is below the northern part of awaji island and reaches down to a depth of 5 km the other region northeast of kobe city is along the arima takatsuki tectonic line and extends along the rokko kashiodani and yamada faults it extends northward to the hokusetsu sanchi area in both regions a high density of fault lineations is mapped and high poisson ratios are known this suggests that partially saturated cracks cause the observed high attenuation

studying deep sources of volcanism using multiscale seismic tomography abstract this paper presents an overview of several examples of multiscale studies of different volcanic systems including intracontinental collisional and subduction related volcanic areas regional tomographic models of the upper mantle are presented for three regions with the cenozoic intracontinental volcanism in eurasia namely europe southern siberia and eastern arctic in all cases recent volcanic fields correlate with low velocity anomalies in the mantle the modeling results show that these volcanic manifestations are related to large hot areas in the mantle and not to thin column shaped contrasted plumes as presumed by many collisional type volcanism is discussed with an example of the caucasus and the surrounding areas the regional tomographic model for this region reveals a lack of mantle lithosphere beneath the collision zone volcanism in this area is most likely due to the direct heating of the thick crust by the hot asthenosphere a dominantly felsic composition of the crust facilitates upward transport of the fluids and melts that leads to volcanic eruption subduction related volcanic systems are discussed for three different scale levels an example of a regional model of the mantle beneath the sunda arc reveals the general configuration of the slab middle scale tomographic models in areas of the toba caldera central java and central andes display feeding paths of the arc volcanoes from the slab the feeding paths are apparent in all of the considered cases but have different shapes depending on the unique features of the subduction regimes an example of a detailed local scale study of magmatic sources in the crust is discussed for the kluchevskoy volcano group it is found that the main volcano kluchevskoy is fed through a complex three layered system of magma sources another volcano of the same group bezymianny seems to be connected with the mantle through a direct short lived channel which appears only during the eruption periods a time dependent tomography study performed for this group over a period of ten years clearly reveals the correlation between the changes in the seismic structures and the stages of the volcanic process namely preparation activation and relaxation

sensitivity of cyclogenesis to sea surface temperature in the northwestern atlantic during the intensive observation period 15 13 15 february 1997 of the fastex experiment a major cyclone crossed the atlantic ocean from the newfoundland basin to southern iceland its surface low center deepened by 17 hpa in 7 h when the perturbation crossed the north atlantic current nac from cold 38c to warm water 158c to elucidate the role of sea surface temperature sst and air sea fluxes in the dynamics of oceanic cyclones three nonhydrostatic mesoscale simulations were performed the first one is a control experiment with a realistic sst field describing in detail the oceanic front associated with the nac system the two following simulations are sensitivity experiments where the sst front is removed the first one uses a uniformly cold sst equal to 38c and the second one uses a uniformly warm sst equal to 158c the frontogenetic function and the vertical velocity sources in the lower atmospheric layers of the three simulations were diagnosed in the control simulation the surface heat fluxes were found to be negative in the perturbation warm sector and positive in the region behind the cold front as reported by numerous authors this pattern of surface heating and cooling did not intensify the cyclone except in the occlusion when the phasing with the sst front occurs this configuration enhances the horizontal gradient of surface buoyancy flux across the occlusion which increases the buoyancy flux source of vertical velocity w when the sst front is removed the surface heat fluxes are strongly affected in magnitude and in spatial variability the marine atmospheric boundary layer mabl stability the convective activity the warm advection in the core of the wave and the heating depth are strongly affected by the different surface flux fields there are several consequences i the uniform ssts tend to decrease the cold front intensity of the wave ii a weaker buoyancy flux source of vertical velocity is found above a uniform cold sst across the occlusion in comparison with the control case and iii surprisingly a weaker w buoyancy flux source is also found above a uniform warm sst because of a higher heating depth vertical velocity depends not only on the buoyancy flux forcing but also on the thermal wind the turbulent momentum and the thermal wind imbalance forcings the thermal wind forcing and the thermal wind imbalance forcing were the most sensitive to the sst compared to the turbulent momentum forcing this result means that i the feed back of the ageostrophic circulation induced by the surface is greater on the kinematic forcings than on the turbulent forcings and ii the turbulent momentum forcing does not play a crucial role in cyclogenesis above a uniform warm sst the strongest intensity of the occlusion is due to the strongest w thermal wind forcing and w thermal wind imbalance forcing in the mabl in spite of a weaker w buoyancy flux forcing than in the control case this result is explained by the convective activity that increases the low level convergence and vorticity spinup this point means that latent heat release and baroclinicity are in tight interaction in the first 12 h and at the scale of the simulation domain the three cyclones evolve similarly but at a small scale their internal structures diverge strongly and rapidly the scale at which the surface turbulent fluxes act on the dynamics of marine cyclones is therefore important finally the cyclone simulated in the warm sst case developed more rapidly than those simulated in the real and the cold sst cases this behavior is attributed to the strong positive surface heat fluxes because they preconditioned the mabl by moistening and heating the low levels during the incipient stage of the cyclone development

inversion tectonics of the variscan foreland of the british isles late westphalian inversion structures on the variscan foreland display wide variations in orientation that are the product of the underlying basement grain the orientation of the major basement lineaments in relation to the direction of maximum shortening also determined the severity of deformation of the inverted basins ne sw trending faults were oriented roughly perpendicular to the nw se to nnw sse direction of maximum shortening determined from thrust transport directions in the variscan orogen to the south as a consequence ne sw trending basins in the variscan foreland have been strongly inverted the silesian post rift fill has commonly been expelled from the basins and the syn rift sediments have been deformed by chevron folds dublin and bowland basins in contrast the n s and nw se trending faults were oriented more obliquely to the direction of maximum shortening and as a consequence display a significant component of oblique slip this oblique slip component is manifested as en echelon periclines and flower structures in general the n s and nw se trending basins were less strongly inverted and the silesian post rift fill has been retained

numerical models of crustal scale convection and partial melting beneath the altiplano puna plateau we employ 2 d thermo mechanical modelling to study possible mechanisms for generating large scale crustal magmas in the altiplano puna region of the central andes the peak of ignimbrite activity in the late miocene and pliocene is associated in space and time with tectonic shortening and plateau uplift a seismic low velocity zone and other geophysical observations indicate that partial melting in the mid crust is still present under the ignimbrite province today we show that neither radiogenic heat production in a thickening crust nor shear heating due to tectonic shortening nor heat brought by intrusions of arc magmas into the mid crust can heat the mid crust to the degree and within the time frame suggested by the geologic petrologic and geophysical observations a viable mechanism to achieve high temperatures within the time constraints is convective heat and mass transfer by partially molten lower crust which itself was heated by enhanced mantle heat flow possibly associated with delamination of the mantle lithosphere during tectonic shortening and intensified magmatic arc activity the thermo mechanical models explain the mid crustal low velocity zone and the high and strongly variable surface heat flow observed in the altiplano convection by bulk flow of the crust appears when the middle and lower crust are mechanically weak quartz dominated rheology the basal heat flow from the mantle is high s 60 mw m 2 and tectonic shortening is active we argue that these conditions are satisfied in the central andes orogen 6 2002 elsevier science b v all rights reserved

a magneto variation array study in the central andes of n chile and sw bolivia during several campaigns long period electromagnetic variation measurements were carried out in the central andes between 19 5 s and 22 s in the convergence zone of the oceanic nazca plate and the continental south american plate a robust multiple station analysis has been used to investigate local differences of geomagnetic variation as an indication of subsurface conductivity distribution for this purpose spatially interconnected arrays of simultaneously running field stations have been further combined to form a large synthetic array the analysis reveals a pronounced ns striking anomaly with a maximum at a period of about hundred seconds in the chilean precordillera which is likely due to the presence of the rather complex precordillera fault system while this anomaly vanishes towards longer periods strong anomalous currents in the bolivian altiplano can be observed within the whole period range indicating a great body of enhanced conductivity underneath

pattern recognition and lithological interpretation of collocated seismic and magnetotelluric models using self organizing maps summary joint interpretation of models from seismic tomography and inversion of magnetotelluric mt data is an efficient approach to determine the lithology of the subsurface statistical methods are well established but were developed for only two types of models so far seismic p velocity and electrical resistivity we apply self organizing maps soms which have no limitations in the number of parameters considered in the joint interpretation our som method includes 1 generation of data vectors from the seismic and mt images 2 unsupervised learning 3 definition of classes by algorithmic segmentation of the som using image processing techniques and 4 application of learned knowledge to classify all data vectors and assign a lithological interpretation for each data vector we apply the workflow to collocated p velocity vertical p velocity gradient and resistivity models derived along a 40 km profile around the geothermal site gros schonebeck in the northeast german basin the resulting lithological model consists of eight classes covering cenozoic mesozoic and palaeozoic sediments down to 5 km depth there is a remarkable agreement between the litho type distribution from the som analysis and regional marker horizons interpolated from sparse 2 d industrial reflection seismic data the most interesting features include 1 characteristic properties of the jurassic low p velocity gradients low resistivity values interpreted as the signature of shales and 2 a pattern within the upper permian zechstein layer with low resistivity and increased p velocity values within the salt depressions and increased resistivity and decreased p velocities in the salt pillows the latter is explained in our interpretation by flow of less dense salt matrix components to form the pillows while denser and more brittle evaporites such as anhydrite remain in place during the salt mobilization

low frequency variability in the midlatitude atmosphere induced by an oceanic thermal front abstract this study examines the flow induced in a highly idealized atmospheric model by an east west oriented oceanic thermal front the model has a linear marine boundary layer coupled to a quasigeostrophic equivalent barotropic free atmosphere the vertical velocity at the top of the boundary layer drives the flow in the free atmosphere and produces an eastward jet parallel to the oceanic front s isotherms a large gyre develops on either side of this jet cyclonic to the north and anticyclonic to the south of it as the jet intensifies during spinup from rest it becomes unstable the most unstable wave has a length of about 500 km it evolves into a meander and eddies detach from the eastern edge of each gyre the dependence of the atmospheric dynamics on the strength t of the oceanic front is studied the gulf stream and kuroshio fronts correspond roughly in the scaling used here to t 7 c for weak fronts t 4 c the circulation is steady and exhibits two large antisymmetric gyres sepa

nonhydrostatic simulations of coastal mesobeta scale vortices and frontogenesis abstract a nonhydrostatic version of the pennsylvania state university national center for atmospheric research mesoscale model with a horizontal resolution of 5 km is used with measurements taken during intensive observation period 2 of the genesis of atlantic lows experiment to study the offshore mesobeta scale coastal front structure results from the 24 h model simulation and doppler radar data indicate that precipitation bands with embedded convective elements are present along the coastal front in the vicinity of the gulf stream as the frontogenesis evolves the simulated surface frontal zone becomes fractured and discontinuous lines of confluence and mesoscale ascent become apparent a collapse of the cross frontal thermal gradient is driven by intense gradients of the surface fluxes in the vicinity of the gulf stream a mesoscale wave train consisting of a series of shallow weak vortices with horizontal scales between 50 and 100 km forms along the front in agreement with the doppler radar

electrical conductivity of the serpentinised mantle and fluid flow in subduction zones in the mantle wedge of subduction zones electromagnetic profiles reveal high electrical conductivity bodies in hot areas 700 degrees c water released by dehydration of the slab induces melting of the mantle under volcanic arcs that can explain the observed high conductivities in the cold 1 m fluids during progressive serpentinisation of the mantle wedge these fluids can mix with arc magmas at depths and account for high chlorine water ratios in arc lavas

imaging fluid related subduction processes beneath central java indonesia using seismic attenuation tomography abstract we use local earthquake data observed by the amphibious temporary seismic meramex array to derive spatial variations of seismic attenuation qp in the crust and upper mantle beneath central java the path averaged attenuation values t of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique these 1929 t values inverted by a least squares tomographic inversion yield the 3d distribution of the specific attenuation qp analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the qp model we notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km most of this anomaly seems to be related to the eocene miocene kendeng basin mainly in the eastern part of the study area enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts presence of fluids and increased temperatures in the middle to upper crust the middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids

sensitivity studies applied to a two dimensional resistivity model from the central andes summary long period magnetotelluric mt data have been collected along an e w profile across the central andes in northern chile and southern bolivia a 2 d resistivity model explaining these data was found by inverse modelling the model includes a prominent conductivity anomaly in the backarc of the south american subduction zone below the bolivian altiplano another comparatively localized anomaly occurs beneath the precordillera in the forearc the enhanced conductivity in the backarc correlates with reflective zones low seismic velocities and high seismic attenuation in contrast no correlation can be found in the forearc a strong seismic reflector in context with the down going slab and another reflector in the middle crust below the pre and western cordillera do not coincide with anomalous conductivity other 2 d models may also be consistent with the data we applied different techniques to find the range of relevant models one simple but useful approach is the direct use of the sensitivity matrix containing the partial derivatives of the data with respect to the model parameters the sensitivity of the model parameters to the data or data subsets can be visualized by calculating columnwise sums from the sensitivity matrix these sensitivities may be used to indicate model parameters that are less resolved by the data and thus should not form part of an interpretation another approach is to perform systematic studies to establish the validity of geologically important features of the model these studies comprise forward modelling and the use of a priori information combining all approaches generates a more complete assessment of the principal model features we conclude that a minimum depth extent of the altiplano conductor can be specified as approximately 50 km low sensitivity in the forearc beneath the longitudinal valley indicates a limited structure resolution and therefore may explain the absence of a conductive slab in the model the existence of the localized conductor below the precordillera can be established by high sensitivity finally we included the two seismic reflectors in the forearc as a priori information in the inversion process as a result the absence of a conductive slab in the model is probably a result of low sensitivity but cannot be totally excluded a conductive zone coinciding with the strong reflector below the pre and western cordillera is not manifested by the mt data

three dimensional models of p wave velocity and p to s velocity ratio in the southern central andes by simultaneous inversion of local earthquake data the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 seismological network of 31 digital broad band and short period three component seismometers was deployed in northern chile between the coastal cordillera and the western cordillera more than 5300 local seismic events were observed in a 100 day period a subset of high quality p and s arrival time data was used to invert simultaneously for hypocenters and velocity structure additional data from two other networks in the region could be included the velocity models show a number of prominent anomalies outlining an extremely thickened crust about 70 km beneath the forearc region an anomalous crustal structure beneath the recent magmatic arc western cordillera characterized by very low velocities and a high velocity slab a region of an increased vp vs ratio has been found directly above the wadati benioff zone which might be caused by hydration processes a zone of lower than average velocities and a high vp vs ratio might correspond to the asthenospheric wedge the upper edge of the wadati benioff zone is sharply defined by intermediate depth hypocenters while evidence for a double seismic zone can hardly be seen crustal events between the precordillera and the western cordillera have been observed for the first time and are mainly located in the vicinity of the salar de atacama down to depths of about 40 km

double seismic zone of the nazca plate in northern chile high resolution velocity structure petrological implications and thermomechanical modeling this paper presents an interdisciplinary study of the northern chile double seismic zone first a high resolution velocity structure of the subducting nazca plate has been obtained by the tomodd double difference tomography method the double seismic zone dsz is observed between 80 and 140 km depth and the two seismic planes is 20 km apart then the chemical and petrologic characteristics of the oceanic lithosphere associated with this dsz are deduced by using current thermal petrological seismological models and are compared to pressure temperature conditions provided by a numerical thermomechanical model our results agree with the common hypothesis that seismicity in both upper and lower planes is related to fluid releases associated with metamorphic dehydration reactions in the seismic upper plane located within the upper crust these reactions would affect material of basaltic morb composition and document different metamorphic reactions occurring within high p 2 4 gpa and low t 130 km lawsonite amphibole eclogite conditions the lower plane lying in the oceanic mantle can be associated with serpentinite dehydration reactions the vp and vs characteristics of the region in between both planes are consistent with a partially 25 30 vol antigorite 0 10 vol brucite and 4 10 vol chlorite hydrated harzburgitic material discrepancies persist that we attribute to complexities inherent to heterogeneous structural compositions while various geophysical indicators evidence particularly cold conditions in both the descending nazca plate and the continental fore arc thermomechanical models indicate that both seismic planes delimit the inner slab compressional zone around the 400 c 50 c isotherm lower plane earthquakes are predicted to occur in the slab s flexural neutral plane where fluids released from surrounding metamorphic reactions could accumulate and trigger seismicity fluids migrating upward from the tensile zone below could be blocked in their ascension by the compressive zone above this plane thus producing a sheeted layer of free fluids or a serpentinized layer therefore earthquakes may present either downdip compression and downdip tensile characteristics numerical tests indicate that the slab s thermal structure is not the only factor that controls the occurrence of inner slab compression 1 a weak ductile subduction channel and 2 a cold mantle fore arc both favor inner slab compression by facilitating transmission of compressional stresses from the continental lithosphere into the slab 3 decreasing the radius of curvature of the slab broadens the depth of inner slab compression whereas 4 decreasing upper plate convergence diminishes its intensity all these factors indicate that if dszs indeed contour inner slab compression they cannot be linked only to slab unbending but also to the transmission of high compressional stresses from the upper plate into the slab

comments on kinematic variations across eastern cordillera at 24 s central andes tectonic and magmatic implications by acocella et al tectonophysics 434 2007 81 92 abstract the interpretation of acocella et al about i westward increase of strike slip motion ii strain partitioning iii symmetry of the central andes as well as iv the interpreted cause for the occurrence of magmatic centres behind the arc from the late miocene onward is largely speculative and contains major flaws we demonstrate all above that successive phases of deformation from middle eocene to quaternary in the edge of the puna eastern cordillera as well as the occurrence of arc intraplate signatures in the magmatic centres of the eastern cordillera result in complex geological framework which requires more detailed and intensive work in order to achieve sustainable interpretations

coincident anomalies of seismic attenuation and electrical resistivity beneath the southern bolivian altiplano plateau 1 reassessment of local earthquake data from the ancorp seismological network allowed the calculation of 3d attenuation qp tomographic images of crust and upper mantle beneath the southern bolivian altiplano around 21 s the images reveal a low qp middle and lower crust and a moderate qp upper mantle beneath the southern altiplano beneath the recent magmatic arc qp is not significantly decreased at this latitude the distribution of crustal qp coincides with the variation of electrical resistivity thus limiting the possible mechanisms causing the anomalies our findings support the hypothesis that partial melts in middle and lower crust beneath the altiplano are present on a large scale we see no evidence for a shallow asthenosphere beneath the southern altiplano

the bolivian altiplano conductivity anomaly 1 a long period magnetotelluric study was carried out in the central andes between latitudes 19 5 s and 21 s along two almost parallel profiles of 220 and 380 km length respectively the investigation area extends from the pacific coast to the southern altiplano plateau in the back arc of the south american subduction zone the main geoelectrical structure resolved is a broad and probably deep reaching highly conductive zone in the middle and deeper crust beneath the high plateau although the data show deviations from two dimensionality a two dimensional approach is justified for large parts of the profiles sensitivity studies were carried out in order to constrain the depth extent another electrically conductive structure was resolved in the middle crust of the chilean forearc thought to be connected with the precordillera fault system the andean continental research program ancorp seismic reflection profile carried out along the same line at 21 s revealed highly reflective zones below the altiplano in good correlation with the upper boundary of the altiplano conductor this highly conductive domain also coincides with low seismic velocities and a zone of an elevated vp vs ratio and although not well resolved with low qp seismic quality factors taking into account the enhanced heat flow and a derived temperature model the most probable explanation lies in the assumption of granitic partial melts the good conductor below the volcanic arc which was found in regions farther south at 22 s gradually vanishes toward the north this is consistent with the results of seismic tomography concerning qp values and a gap of recent volcanism

attenuation tomography in the western central andes a detailed insight into the structure of a magmatic arc high quality data from 1498 local earthquakes recorded by the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 and ancorp 96 andean continental research project 1996 temporary seismological networks allowed the detailed determination of the three dimensional 3 d attenuation structure qp 1 beneath the recent magmatic arc in the western central andes 20 to 24 s assuming a frequency independent qp 1 in a frequency band between 1 and 30 hz whole path attenuation t was estimated from the amplitude spectra of the p waves using spectral ratios and a spectral inversion technique the damped least squares inversion tomography of the data reveals a complex attenuation structure crust and mantle of the forearc and subducting slab are generally characterized by low attenuation qp 1000 crust and mantle beneath the magmatic arc show elevated attenuation the strongest anomaly of extremely low qp is found in the crust between 22 and 23 s beneath the recent volcanic arc qp 100 n s variations can be observed the western flank of the crustal attenuation anomaly follows the curved course of the volcanic front north of 21 s the attenuation is less developed in the northern part of the study area the low qp zone penetrates in the forearc mantle down to the subducting slab in the south a deeper zone of high attenuation is resolved between 23 and 24 s directly above the subducting slab low qp in the mantle correlates with earthquake clusters the strong crustal attenuation is confined to the distribution of young ignimbrites and silicic volcanism and is interpreted as a thermally weakened zone with partial melts the attenuation pattern in the upper mantle might reflect the variable extent of the asthenosphere and maps variations of subduction related hydration processes in the mantle wedge from slab derived fluids

the influence of partial melting on the electrical behavior of crustal rocks laboratory examinations model calculations and geological interpretations abstract the complex electrical impedance of a granulite has been determined over the frequency range 10 1 to 105 hz at temperatures between 600 and 1200 c at normal pressure and different oxygen fugacities in the stability field of magnetite the impedance spectroscopic is measurements are compared with the results of melting experiments performed under the same experimental conditions and with the same rock sample as the is measurements a strong increase in the electrical conductivity of about one and a half orders of magnitude is observed during partial melting this increase is explained by the formation of an interconnected network of melt the wetting of the grain surfaces starts slightly above the solidus however complete interconnection of the network is detected at higher temperatures 1070 c and hence higher melt fractions 10 vol this is explained by deviations from the equilibrium fabric of the partially molten sample with a modified brick layer model mblm the electrical conductivity is calculated as a function of the observed melt portion this model is valid if the melt forms a complete interconnected network at the grain boundaries the electrical conductivity at different temperatures was modeled using the results of the melting experiments and the mblm melt 10 s m with ea melt 1 ev solid 0 01 s m with ea solid 1 4 ev the results of the laboratory examinations were applied to different crustal regions where partially molten rocks are assumed to exist the same mblm is used to estimate the melt fraction that is necessary to explain the high conducting zones hczs observed in the crust beneath the andean orogen the pyrenees and the tibetan plateau at least 14 4 and 4 vol of interconnected melt are necessary to produce the observed conductivity respectively the actual amount of melt should be higher due to perturbation problems and melt trapped in pockets

magnetotelluric images of magma distribution beneath volcan uturuncu bolivia implications for magma dynamics the altiplano puna volcanic complex in the central andes records a history of major caldera forming eruptions over the past 10 m y geophysical and geodetic data indicate that magma is still present and perhaps mobile in the crust broadband magnetotelluric data were used to generate two dimensional and three dimensional electrical resistivity models of the altiplano puna magma body apmb with a focus on the zone of inflation around volcan uturuncu in southern bolivia low electrical resistivities 20 the upper surface of the apmb is shallowest beneath uturuncu and the geometry is consistent with geodynamic models that require the upward movement of a melt layer at this location the shallower resistivity structure is characterized by discrete electrically conductive bodies oriented east west near sea level depth of 5 km which are interpreted as a combination of partial melt and fluids

electrical conductivity beneath the bolivian orocline and its relation to subduction processes at the south american continental margin 1 a long period magnetotelluric data set was obtained during 2002 and 2004 in the central andes to study the deep electrical conductivity structure in the region of the bolivian orocline between latitudes 17 s and 19 s the profile extends from the coastal cordillera in northernmost chile crosses the volcanic arc and the altiplano high plateau in central bolivia and ends in the eastern cordillera two dimensional inversion revealed several well defined conductivity anomalies in upper crustal levels the conductive sedimentary basins of the central altiplano and the resistive arequipa block beneath the western altiplano are imaged earlier seismological and magnetotelluric investigations on the southern altiplano inferred a large highly conductive partially molten body in the mid to deep crust it was assumed that this structure would be underlying the entire plateau but this is not the case according to the new models instead the most prominent feature in the new investigation area is a high conductivity zone at upper mantle depths below the high plateau which may be interpreted as an image of partial melts and fluids triggered by water supply from the subducting nazca slab this conductor would be in accordance with the standard subduction scenario it is however laterally offset by almost 100 km from the volcanic arc in contrast the deep crust and upper mantle beneath the arc is moderately resistive both observations may hint at an emerging shift of the magmatic fluid system in the central andes

the central andean altiplano puna magma body receiver function analysis of 14 teleseismic events recorded by 6 temporary passcal broadband stations within the altiplano puna volcanic complex apvc shows a consistent 2 s negative polarity p to s conversion for all stations for all available azimuths forward modeling of the largest amplitudes suggests that this conversion is produced by the top of a very low velocity zone at a depth of 19 km with a vs 0 5 km s and a thickness of 750 810 m we interpret the characteristics of the low velocity zone low vs areal extent and flatness to be consistent with a sill like magma body on the basis of additional data from the german ancorp experiment the altiplano puna magma body appears to underlie much of the apvc and it may therefore be the largest known active continental crustal magma body

seismic gravity and petrological evidence for partial melt beneath the thickened central andean crust 21 23 s on the basis of seismic refraction investigations and gravimetric data we have modelled the crustal structure of the southern central andes 21 23 s a pronounced variation in crustal parameters is seen in n s and w e crossing seismic profiles over the entire andean orogene characterized by a crustal thickness of up to 70 km under the magmatic arc and backarc strongly reduced seismic velocities and a bouguer minimum of 450 mgal anomalously low velocities of 5 9 6 0 km s in the deeper crust of the western cordillera and altiplano regions lead to an over compensation of the bouguer minima resulting in values of crustal densities higher than estimates based purely on seismic velocity measurements in an attempt to reconcile these differences the behavior of crystalline rocks based on published laboratory data was studied under varying pressure and temperature conditions up to the range of partial melting if the temperature is increased above the melting point a rapid decrease in seismic velocity is accompanied by a slow decrease in density for the central andes a good fit of the observed and calculated bouguer anomalies is obtained if the densities of the rocks from the low velocity zone lvz beneath the western cordillera and the altiplano are varied model calculations lead to a velocity density relation for partial molten rocks that allows the melt proportions of rocks to be estimated model calculations indicate that 15 20 vol of basaltic to andesitic melt at depth is necessary to explain the lvz and bouguer anomaly beneath the arc and parts of the backarc high heat flow values 100 mw m2 support the idea that large areas of the deeper andean crust are strongly weakened by the presence of partially molten rocks resulting in reduced seismic velocities with the western cordillera the active volcanic arc of the andean mountain range acting as a ductile buffer between the two more rigid crustal blocks of the forearc and backarc regions

composition and thickness of the southern altiplano crust bolivia slant stacking of broadband seismograms recorded in the western united states for two 1993 intermediate depth earthquakes that occurred near the bolvia argentina chile borders reveals small but clear precursors to both the compressional p wave and shear s wave depth phases we interpret and model these precursors as underside reflections from the thickened andean altiplano crust we model the crustal structure of the altiplano with a grid search technique to match the timing and amplitudes of the depth phases and precursors in the waveforms of both the p wave and s wave our best fit model has an average crust velocity of 5 9 6 0 km s a crustal v sub p v sub s of 1 6 a crustal thickness of 75 80 km and a high velocity v sub p 8 4 km s high v sub p v sub s 1 9 mantle wedge assuming isotropy the low v sub p v sub s ratio of 1 6 for the crust corresponds to an anomalously low poisson s ratio of 0 18 such a low value in conjunction with the low average v sub p estimate is consistent only with a felsic composition and high upper crustal temperatures the finding of a thick felsic crust overlying a high velocity mantle supports models of altiplano uplift due predominantly to crustal shortening as opposed to mafic magmatic additionmore and is inconsistent with recent mantle delamination 19 refs 3 figs 1 tab less

three dimensional density model of the nazca plate and the andean continental margin 1 we forward modeled the bouguer anomaly in a region encompassing the pacific ocean 85 w and the andean margin 60 w between northern peru 5 s and patagonia 45 s the three dimensional density model that reproduces the gravity field is a continental scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic nazca plate subducted slab and continental margin with a minimum number of bodies we predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure temperature conditions appropriate for the andean setting a database of independent geophysical information constrains the geometry of the top of the subducted slab locally the moho of the oceanic and continental crusts and indirectly the lithosphere asthenosphere boundary underneath the continental plate other boundaries notably the intracrustal density discontinuity separating upper from lower crust below the continent were not constrained and their geometry is the result of fitting the observed and calculated bouguer anomaly during forward modeling this contribution presents the model to the andean geoscientific community and contains some tools like a sensitivity analysis that helps potential users of the model to interpret its results we describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena e g modification of oceanic plate structure by hot spots shape of the subducted slab thermal structure of the continental lithosphere compensation mechanism and formation of orogenic relieve causes of andean segmentation

effective elastic thickness variations along the andean margin and their relationship to subduction geometry 1 we present a new map of the spatial variations in effective elastic thickness te along the andes estimated using bouguer coherence the te variations reflect interactions between subducting slab and preexisting terrane structure in the forearc conductive cooling of the continent by the subducting slab exerts primary control on rigidity resulting in te that is highest 40 km where the oceanic lithosphere is oldest and coldest 20 s in the central andes te is relatively low 20 km along the volcanic chain and the altiplano and puna plateaus we interpret this weakening to reflect a high geothermal gradient maintained by advective magmatic processes a shallow and hot asthenosphere and a very weak lower crust throughout this region east of the plateaus high te delineates underthrusting of the brazilian shield finally north and south of the plateaus flat subduction areas are characterized by high te high shear wave velocity thick thermal lithosphere and low heat flow indicating that continental lithosphere there is thicker colder and stronger on the basis of these relationships we suggest that variations in slab dip along the margin relate to variations in structure of the continental lithosphere in particular we propose that upper plate structure influences the width and viscosity of the asthenospheric wedge which control the suction moment responsible for the subduction angle at depths 70 100 km for example when oceanic lithosphere subducts beneath thin continental lithosphere the low viscosity asthenosphere allows the slab to detach from the continent and sink into the mantle at normal angles however when oceanic lithosphere subducts close or beneath thick and strong continental lithosphere the asthenospheric wedge narrows and corner flow drags high viscosity mantle from the base of the thick 150 km cold continent into the wedge suction forces increase with both narrowing of the wedge and its increasing viscosity we estimate the asthenospheric viscosity underneath thick cold continents to be 1020 pa s sufficient to induce flat subduction later after prolonged hydration and weakening of the continent s base asthenospheric flow into the wedge may resume allowing the slab to sink again into the mantle at normal angles

the nature of orogenic crust in the central andes 1 the central andes 16 22 s are part of an active continental margin mountain belt and the result of shortening of the weak western edge of south america between the strong lithospheres of the subducting nazca plate and the underthrusting brazilian shield we have combined receiver function and surface wave dispersion results from the banjo seda project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure the major results are as follows 1 the crust supporting the high elevations is thick and has a felsic to intermediate bulk composition 2 the relatively strong brazilian lithosphere is underthrusting as far west 65 5 w as the high elevations of the western part of the eastern cordillera ec but does not underthrust the entire altiplano 3 the subcrustal lithosphere is delaminating piecemeal under the altiplano ec boundary but is not completely removed beneath the central altiplano the altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation leading to lower crustal flow and flat topography in contrast in the high relief inland sloping regions of the ec and sub andean zone the upper crust is still strongly coupled across the basal thrust of the fold thrust belt to the underthrusting brazilian shield lithosphere subcrustal shortening between the altiplano and brazilian lithosphere appears to be accommodated by delamination near the altiplano ec boundary our study suggests that orogenic reworking may be an important part of the felsification of continental crust

pure and simple shear plateau uplift altiplano puna argentina and bolivia abstract the concepts of pure and simple shear strain provide a meaningful way of discussing the alternative modes of lithospheric shortening which produced uplift of the central andean plateau since 10 ma discrete segments of the plateau exemplify pure or simple shear modes characteristics of the simple shear mode are a flanking thin skinned thrust belt and subdued relief and lack of significant late miocene to recent deformation within the plateau the pure shear mode is characterized by more rugged internal relief and active neotectonic deformation within the plateau and thick skinned foreland deformation involving seismic deformation of the crust to 30 km or more these modes of crustal thickening correlate with changes in lithosphere thickness modes of isostatic compensation broad wavelength topography and back arc magmatism the correlation of the boundary between pure and simple shear segments with major changes in pre existing anisotropies in the foreland of the orogen suggests that events which long pre date the andean orogeny indirectly controlled the along strike variation in the magnitude and style of shortening in the central andes and may have influenced the development of flat subduction

p and s wave attenuation tomography of the japan subduction zone we determine the first high resolution p and s wave attenuation q tomography beneath the entire japan islands using a large number of high quality t data collected from p and s wave velocity spectra of 4222 local shallow and intermediate depth earthquakes the suboceanic earthquakes used in this study are relocated precisely using sp depth phases significant landward dipping high q zones are revealed clearly which reflect the subducting pacific slab beneath hokkaido and tohoku and the subducting philippine sea phs slab beneath sw japan prominent low q zones are visible in the crust and mantle wedge beneath the active arc volcanoes in hokkaido tohoku and kyushu which reflect source zones of arc magmatism caused by fluids from the slab dehydration and corner flow in the mantle wedge our results also show that nonvolcanic low frequency earthquakes lfes in sw japan mainly occur in the transition zone between a narrow low q belt and its adjacent high q zones right above the flat segment of the phs slab this feature suggests that the nonvolcanic lfes are caused by not only fluid affected slab interface but also specific conditions such as high pore pressure which is influenced by the overriding plate

inferring water infiltration in the longtan reservoir area by three dimensional attenuation tomography summary high resolution 3 d qp and qs models at depths of 0 14 km in the longtan reservoir area which were used to further infer the water infiltration around the reservoir were constructed by the local earthquake tomography technique the inversion used t values measured from velocity spectral amplitudes of 16 134 p wave and 17 027 s wave observations of 2828 events recorded by 23 digital seismic stations in the longtan reservoir area 3 d qp and qs tomographic images suggest a close relation between the attenuation models and water infiltration low qp and qs exist down to 4 7 km depths beneath the main rivers in the reservoir area whereas high qp and qs are found both at deep layers and at shallow layers in regions other than the main river area we inferred that the rocks beneath the main rivers are infiltrated by substantial water and water infiltration reaches 4 7 km deep and the ranges of water infiltration vary by region specifically the zone of high water content is estimated to extend up to 10 km away from the buliu river in the reservoir dam area where water depth in the reservoir reaches maximum and the extent of water infiltration in rocks can only be about 5 km around from the hongshui river and the youla river low qp and high qs indicate that the carbonate rocks in the east of the bala fault area may be saturated with water earthquake clusters are mainly concentrated on the low qp and low qs zones indicating that water infiltration beneath the main rivers possibly plays an important role in inducing earthquakes in the longtan reservoir area

three dimensional attenuation structure of central and southern south island new zealand from local earthquakes 1 the three dimensional attenuation properties of the south island new zealand are obtained from local earthquake t spectral decay data we extend the spectral fitting method used to obtain t by enabling limited frequency dependence for q observed qp heterogeneity relates to both active geological processes and to constituent tectonic blocks with high qp for the haast schist the most pronounced low qp features in the upper crust correspond to zones of recent seismicity rather than the most significant faults the central alpine fault a dipping oblique slip fault forms the western boundary to a low qp volume in the ductile crust particularly low qp is imaged at the base of the alpine fault at 30 km depth and may be related to metamorphic fluid release in the crustal root a region of predicted high strain conversely the southern alpine fault which is a vertical strike slip fault forms the western boundary to the high qp schist region in the southern south island the plate boundary becomes a subduction zone exhibiting unusual qp character moderately high qp is associated with the subducted australian plate there is also a high qp high vp feature in the pacific mantle to 160 km depth that appears to cause the subducting slab to bend to near vertical this feature may represent mantle shortening since the miocene regional attenuation rates for fiordland earthquakes calculated from the 3 d qp model show large variations over the south island the low qp in the crustal root has a significant effect on passing raypaths

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

complex patterns of fluid and melt transport in the central andean subduction zone revealed by attenuation tomography abstract we present a high resolution 3 d model of p wave attenuation q p 1 for the central andean subduction zone data from 1500 mostly intermediate depth 60 250 km earthquakes recorded at three temporary seismic networks covering the forearc arc and backarc around 23 s were used for tomographic inversion the forearc is characterised by uniformly high q p values indicating low temperature rocks in accordance with low surface heat flow values prominent low q p anomalies are found beneath the magmatic arc and the backarc in the crust and mantle continuous regions of low q p connect earthquake clusters at 100 km and 200 km depth with zones of active volcanism in the arc and backarc fluids fluxed from the subducted oceanic lithosphere into the overlying mantle wedge where they induce melting explain our observations we propose that low q p regions indicate source and ascent pathways of metamorphic fluids and partial melts ascent of fluids and melts as imaged by seismic q p are not vertical as is often implicitely assumed instead sources of fluids are located at different depth levels and ascent paths are complex and exhibit significant variation within the study area the largest quaternary backarc volcano cerro tuzgle is fed by mantle melts which are imaged as a plume of low q p material that reaches to the strong earthquake cluster at 200 km depth

end member models for andean plateau uplift abstract diverse techniques have been applied over the past decade to quantify the uplift history of the central andean plateau ap in this study opposing models for surface uplift are evaluated including a rapid rise of 2 5 km 10 6 ma and a slow and steady rise since 40 ma these end member models are evaluated by synthesizing observations of the ap lithosphere and the history of deformation sedimentation exhumation magmatism uplift and fluvial incision structural and geophysical studies estimate variable shortening magnitudes 530 150 km involving cover to basement rocks an isostatically compensated thick crust 80 65 km high heat flow and zones of variable velocity and attenuation in the crust and mantle these observations have invoked interpretations such as a hot weak lithosphere partial melt crustal flow and perhaps current localized delamination but do not provide strong support for massive delamination required by the rapid uplift model deformation and associated exhumation began 60 40 ma and generally migrated eastward with consistent long term average shortening rates 12 8 mm yr in bolivia favoring the slow uplift model volcanic and helium isotope evidence show an ap wide zone of shallow mantle melting and thin lithosphere that has existed since 25 ma which is inconsistent with the rapid rise model that suggests lithospheric thinning occurred 10 6 ma paleoaltimetry data suggest a rapid 2 5 km elevation gain 10 to 6 ma but are equally consistent within error with a linear rise since 25 ma widespread fluvial incision 2 5 1 km occurred along the western flank since 11 8 ma and may be associated with surface uplift as proposed by the rapid rise model however the paleoaltimetry and incision data can also be explained by regional climate change associated with plateau uplift implications of these results for reconstructions of ap evolution are that 1 substantial deformation of a weak lithosphere is essential 2 ap growth has taken significantly longer 40 myr and was more uniform along strike 1500 km than previously appreciated and 3 the slow and steady uplift model is most consistent with available constraints we conclude that the rapid uplift model may be an overestimate and that a more protracted cenozoic uplift history is tenable

a new analytical solution estimating the flexural rigidity in the central andes summary we present a new 2 d analytical solution of the fourth order differential equation which describes the flexure of a thin elastic plate the new analytical solution allows the differential equation for an elastic plate to be solved for any irregular shaped topography with a high spatial resolution we apply the new method to the central andes the flexural rigidity distribution calculated by this technique correlates well with tectonic units and the location of fault zones for example the central andean gravity high correlates with the presence of a rigid high density body