lithospheric structure and along strike segmentation of the central andean plateau seismic q magmatism flexure topography and tectonics the central andean plateau is a 300 km wide nearly 4 km high plateau which is situated above a 30 e dipping segment of the subducted nazca plate systematic changes in the topography the upper mantle seismic attenuation q structure the lithospheric flexural rigidity and the distribution and chemistry of back arc lavas indicate that the upper mantle structure changes along strike beneath the plateau south of 23 s the upper mantle beneath the plateau becomes hotter and the lithosphere becomes thinner and weaker this lateral variation in upper mantle structure coincides with variations in the tectonic style and timing of deformation in two physiographically distinct segments of the 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 the segments different mantle lid thicknesses result in an altiplano supported mainly by crustal thickening and a puna supported by a combination of a crustal root and a thermal mantle root a thicker stronger foreland lithosphere in the north favors thin skinned underthrusting of the foreland beneath the plateau while to the south the thinner weaker lithosphere allows more basement involved shortening within the foreland and less underthrusting beneath the plateau a weaker lithosphere results in a longer period of compressional deformation and greater local and structural relief in the puna than in the relatively stable altiplano to the north ultimately this observed n s directed segmentation on the plateau and in the foreland may reflect the different responses of strong and weak continental lithosphere to an andean type subduction margin

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

tidal mixing and trapping in mangrove swamps lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove fringed tidal rivers in the dry season the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude from its value in the absence of swamps in the wet season freshwater is trapped within the swamp and the adjoining boundary in the tidal river for long periods following the passage of a short lived flood this may have important ecological implications a fluid mud layer appears to be created by strong tidal currents over colloidal mangrove mud

outwelling from tropical tidal salt flats abstract the norman river flows into the gulf of carpentaria north east australia the estuary is surrounded by 250 km2 of vegetation free saline supratidal mud flats which are only inundated by the tides at spring high tide in summer when the seasonal sea level is 0 5 1 m higher than in winter the first summer tidal inundation of the salt flats in november 1985 resulted in a readily measurable export from the salt flats of salt and nutrients outwelling values of 90 g salt m 2 per tidal cycle 1 0 mmol silicate m 2 and 3 10 2 mmol orthophosphate m 2 were measured about a quarter of the 4000 km2 of salt flats along the southern shore of the gulf of carpentaria outwell into the gulf the rest outwell into the estuaries where salt outwelling increases the strength of the salinity maximum zone of the estuaries further isolating the rivers from the gulf during the dry season

volcanology history and myths of the lake albano maar colli albani volcano italy abstract the polygenetic albano maar is the most recent centre of the colli albani volcano located just few kilometres to the south east of roma presently the maar hosts a 167 5 m deep crater lake the deepest in europe the maar is to be considered quiescent as phreatic activity is documented throughout the holocene this paper illustrates the close relationships between the activity of the maar and the history of settlement in the roman region as recorded in the geology archaeology history and legends of the area severe fluctuations of the groundwater table and catastrophic overflows of the lake albano from the maar rim had occurred prior to and after the early prehistoric settlements dated in the maar area at the eneolithic times ca iii millennium b c repeated lahars occurred along the northwestern slope of the maar filling in the paleodrainage network and forming a vast plain paleohydraulic analyses on fluvial and lahar deposits originated from the holocene phreatic activity of the albano maar indicate sediment water flows in excess of hundreds of cubic metres per second absolute age determinations of the paleosoil underlying one of the most recent deposits of the lahar succession at 5800 100 yr b p 14 c cal are in perfect agreement with the age of the overlying eneolithic age settlements the last catastrophic overflow is described in the roman literature as a consequence of the anger of poseidon against the romans in 398 b c for their war against the etruscans in 394 b c the romans decided to prevent the repetition of such events by the excavation through the maar crater wall of a 1 5 km long drain tunnel which is still operational keeping the lake 70 m below the lowest point of the maar rim this tunnel drain may be regarded as the first prevention device for volcanic hazard in history and shows an unprecedented development of the engineering technology under the pressure of hazard perception the surprising and still largely unknown results of this study are very important to redefine the hazard of the roman region

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

deflection of dykes into sills at discontinuities and magma chamber formation abstract many rift zones contain composite volcanoes central volcanoes most of which are supplied with magma from shallow crustal magma chambers volcanotectonic studies of eroded rift zones such as in iceland as well as geophysical studies indicate that many shallow magma chambers evolve from sills here i provide field description of sills and extinct magma chambers in the quaternary and tertiary palaeorift zones of iceland focusing on the felsic pluton of slaufrudalur southeast iceland as a fine example of a magma chamber developed through the injection of sills in this paper i review analyse and develop further two related mechanisms for the deflection of dykes into sills and thus the potential initiation of a magma chamber namely a cook gordon debounding delamination and b stress barriers and propose a third mechanism c favourable material toughness ratios due to elastic mismatch difference in young s moduli or stiffnesses of layers in contact in the cook gordon mechanism a weak contact opens up as a result of dyke induced tensile stress this mechanism is likely to operate primarily at shallow depths as is supported by field observations and numerical models a stress barrier is a layer where the local stress is unfavourable to a particular type of rock fracture here a dyke field observations and numerical models show that on meeting a stress barrier a dyke either changes into a sill or becomes arrested the material toughness mechanism indicates that when the upper layer at a contact has the same or less stiffness than the lower layer hosting the dyke there is little tendency for the dyke to become deflected into the contact however when the upper layer is stiffer such as when a stiff basaltic lava flow is on the top of a soft pyroclastic layer the dyke tends to become deflected into the contact to form a sill field results suggest that all these mechanisms may cause dyke deflection into sills and may operate together particularly where the rock consists of alternating soft and stiff layers since the quaternary lava pile in iceland has many more soft hyaloclastite layers than the tertiary lava pile these mechanisms were probably very efficient in generating sills and by implication shallow magma chambers during the quaternary this may be one reason why in comparison with the tertiary lava pile the quaternary lava pile contains so many sills and extinct plutons and active shallow magma chambers

polygenetic quaternary volcanism at crater flat nevada abstract alkali basalts erupted during the quaternary at crater flat nevada record a complex history of polycyclic and polygenetic volcanism magmas from the two main centers black cone and red cone are petrographically and geochemically similar although field evidence suggests a number of separate eruptive events high incompatible element concentrations low nb la and high zr y indicate that the magmas were derived by small degrees of partial melting from the lithospheric mantle at red cone a significant range of sr la ce ba and th concentrations is observed with time e g sr range 1308 1848 ppm the youngest samples having the more elevated values however there is only limited variation in the compatible trace elements e g sc and ni the array of compositions at red cone could not have been produced by changes in the degree of partial melting or by fractional crystallization rather a model of magma mixing is proposed between relatively enriched and depleted end members the cluster of black cone data falls consistently at the least enriched end of the red cone sample arrays suggesting that the black cone magma represents one of the mixing end members the modeling indicates that the magmatic plumbing systems of the two centers were linked at least during the early stages of volcanism moreover volcanic activity may have occurred at a number of sites along the length of the magmatic feeder zone during a single eruptive phase this could have significant implications for volcanic hazard assessment in the region around yucca mountain and the proposed nuclear waste repository

backazimuth estimation reliability using surface wave polarization 1 backazimuth estimates derived from surface wave polarization can be used to test association of an observed surface wave with a seismic event however commonly used techniques for estimating the backazimuth are subject to a number of errors and are often inaccurate we evaluate the performance of a new algorithm for determining rayleigh wave propagation direction from the cross correlation of the horizontal and hilbert transformed vertical seismograms this proves to be more accurate and much less error prone than current automatic processing procedures and the cross correlation value provides a good measure of the reliability of the backazimuth estimate consequently the new algorithm will permit more reliable event association at a lower magnitude threshold

an automated rayleigh wave detection algorithm abstract the desire to operate denser networks in order to monitor seismic activity at lower thresholds leads to greater emphasis on automated data processing an algorithm for detecting and characterizing long period rayleigh wave arrivals has been developed and tested the routine continuously monitors all directions of approach to a station in a manner similar to beamforming the detector is based on cro ss powers between the hilbert transformed vertical and rotated horizontal signals so it is sensitive to both the power and polarization properties of the three component wavefield elliptically polarized rayleigh arrivals are enhanced while linearly polarized love waves and body phases are suppressed a test using one month of data from station anmo demonstrated that this technique can with high reliability detect rayleigh arrivals which would be visible to an analyst the measured arrival times and azimuths are accurate enough to permit automated association of the detections to events in a bulletin

the 1245 yr bp asososca maar eruption the youngest event along the nejapa miraflores volcanic fault western managua nicaragua abstract the asososca tephra comprises the asymmetrically distributed well stratified phreatomagmatic products of the 1245 125 120 yr bp asososca maar eruption west of managua nicaragua it is the youngest eruptive unit related to the monogenetic volcanism concentrated along the n s trending nejapa miraflores active fault and intersecting e w to ne sw and nw se minor faults the close relationship between monogenetic volcanism and the structural local tectonic framework is evidenced by the lineament domains and vent alignment patterns identified by remotely sensed images and dems of the research area the asososca maar lake bathymetry suggests that the crater was formed by coalescing vents migrating during the eruptive event the asososca tephra dominantly consists of accidental lithics disrupted from the underlying stratigraphic units observed inside and around the maar crater dry base surge bedsets are dominant throughout the eruptive unit showing facies variation from proximal cross stratified beds to mid distal plane parallel and wavy parallel beds grain size analyses indicate that base surges transported dominantly 1 0 and 1 sized particles at the bedload in form of traction carpets while fine ash material in continuous suspension was minimal juvenile fragments were only identified in the finer fractions varying from vesiculated scoriae to dense sideromelane fragments sem analyses suggest that the asososca eruption resulted from a highly efficient fuel coolant interaction between a tholeiitic basaltic melt and an aquifer hosted in a shallow level between 50 and 200 m of olivine bearing scoria ash and lapilli beds the explosion triggered the country rock comminution and the production of moss like fused shaped and blocky ash shards with stepped surfaces quenching cracks pitting alteration skins and adhered particles all indicative of phreatomagmatic fragmentation the very recent age of the asososca maar eruption confirms that the densely inhabited managua area is volcanically active and that hazard studies should focus on the potential for phreatomagmatic eruptions

lithofacies association and stratigraphy of the paredao volcano trindade island brazil abstract a stratigraphic framework can be constructed through lithofacies description and interpretation the application of this method in volcanic systems is a fundamental tool for understanding their evolution and eruptive dynamics and for establishing hazard assessments in active volcanic areas this work presents and discusses a detailed stratigraphy of the paredao volcano allowing the understanding of the lateral and vertical distribution of volcanic facies and the 3d geometry of the deposits generating a model for the volcanism and discussing the erupting mechanisms the paredao volcano is a scoria cone located in the southeast of trindade island and represents the youngest subaerial volcanic episode pleistocene recorded in brazil its stratigraphic organization indicates nephelinitic flows alternate with lapillistones and lapilli tuffs of same composition at the base and a pyroclastic cone with nearly 200 m high above the sea level through lithofacies description and association 4 stratigraphic columns were constructed in scale 1 50 three of them at the tartarugas beach trv 01 trv 02 trv 03 and the other one at the pyroclastic cone trv 04 the petrographic characterization of facies was carried through conventional optical microscopy the stratigraphic analysis resulted in the distinction of seven lithofacies divided into two coherent and five volcaniclastic one autoclastic and four pyroclastic the coherent lithofacies are of massive npm and vesicular porphyritic nephelinite npv texturally the lavas are holocrystalline and vesicular composed by olivine phenocrysts in a very fine matrix of clinopyroxene nepheline zeolite and titanomagnetite at times with phlogopite the autoclastic lithofacies of nephelinitic breccia nb is composed of fragments 2 mm 15 cm of vesicular nephelinite and the pyroclastic ones are composed mainly of lapillitic scoria fragments with subordinate bombs and volcanic ash the pyroclastic lithofacies are of massive lapillistone lm and lapilli breccia lbm planar stratified lapilli tuff ltp and reverse grading lapillistone lrg the lithofacies associations characterize a a rubbly pahoehoe and pahoehoe flow types distal and proximal pyroclastic deposits the interpretation of the vertical and lateral facies distribution leads to the conclusion that the volcanism occurred with an initial phreatomagmatic stage succeeded by a strombolian stage pyroclastic with primary fragments domain and a final hawaiian stage lava flows domain

late cenozoic tectonism collapse caldera and plateau formation in the central andes abstract the evolution of andean volcanism including the formation of late miocene to recent collapse calderas on the puna plateau is generally interpreted in terms of the kinematic framework of the nazca and south american plates we present evidence that caldera dynamics and associated ignimbrite volcanism are genetically linked to the activity of first order nw se striking zones of left lateral transtension on the local and regional scales consequently ages of collapse calderas indicate activity of these fault zones which initiated at about 10 ma on the puna plateau the onset of such faulting points to a change in the deformation regime from dominantly vertical thickening to orogen parallel stretching upon reaching maximum crustal thickness and critical surface elevation horizontal magma sheets that formed at mid crustal level possibly due to heat advection by volume increase of asthenospheric mantle below thickened crust were tapped by sub vertical faults this accounts well for the observed tectono magmatic phenomena at surface it follows that formation of collapse calderas and eruption of voluminous ignimbrites appear to be related to the mechanical evolution of the andean plateau rather than to changes in the geometry of the wadati benioff zone or plate boundary kinematics

volcanology and eruptive styles of barren island an active mafic stratovolcano in the andaman sea ne indian ocean barren island india is a relatively little studied little known active volcano in the andaman sea and the northernmost active volcano of the great indonesian arc the volcano is built of prehistoric possibly late pleistocene lava flows dominantly basalt and basaltic andesite with minor andesite intercalated with volcaniclastic deposits tuff breccias and ash beds deposited by pyroclastic falls and surges which are exposed along a roughly circular caldera wall there are indications of a complete phreatomagmatic tephra ring around the exposed base of the volcano a polygenetic cinder cone has existed at the centre of the caldera and produced basalt basaltic andesite aa and blocky aa lava flows as well as tephra during historic eruptions 1787 1832 and three recent eruptions 1991 1994 95 2005 06 the recent aa flows include a toothpaste aa flow with tilted and overturned crustal slabs carried atop an aa core as well as locally developed tumuli like elliptical uplifts having corrugated crusts based on various evidence we infer that it belongs to either the 1991 or the 1994 95 eruptions the volcano has recently 2008 begun yet another eruption so far only of tephra we make significantly different interpretations of several features of the volcano than previous workers this study of the volcanology and eruptive styles of the barren island volcano lays the ground for detailed geochemical isotopic and petrogenetic work and provides clues to what the volcano can be expected to do in the future

effect of strain rate in the distribution of monogenetic and polygenetic volcanism in the transmexican volcanic belt in the transmexican volcanic belt polygenetic and monogenetic volcanism has taken place concurrently with extensional deformation since the late miocene at a regional scale the deformation is manifested by two groups of faults the dominant group consists of normal faults nearly parallel to the arc in the other group are north northwest trending normal faults that cross the arc and in places form the boundaries of crustal blocks the larger stratovolcanoes of the transmexican volcanic belt are aligned in north south volcanic chains along some of these faults whereas monogenetic volcanoes are usually located along arc parallel normal fault systems because the arc parallel faults are 15 oblique to the subduction plate boundary and assuming stretching perpendicular to the trench the extensional deformation field facilitates activation of both arc parallel and arc transverse structures the former having a higher displacement rate than the latter we observe that in the transmexican volcanic belt polygenetic volcanoes develop along faults having small strain rate and monogenetic volcanoes are emplaced along faults having higher strain rate the agreement with the theoretical model in which monogenetic or polygenetic volcanism depends on the magmatic input rate and the regional stress is true only assuming a linear relation between regional differential stress and local strain rate as in a continuous and homogeneous medium we propose that the local strain rate rather than the regional stress field controls the coexistence of both types of volcanism in the transmexican volcanic belt

methods for amplitude calibration and orientation discrepancy measurement comparing co located sensors of different types in the southern california seismic network modern seismic networks commonly equip a station with multiple sensors to extend the frequency band and the dynamic range of data recorded at the station in addition in our recent study we showed that comparison of data from co located seismometers and accelerometers is useful for detecting instrument malfunctions and monitoring data quality in this study we extend comparison of data from different co located sensors to two other applications 1 amplitude calibration for data from vertical short period sensors with strong motion sensors as baseline and 2 measurement of orientation discrepancy between strong motion and broadband sensors we perform systematic analyses of data recorded by the california institute of technology u s geological survey southern california seismic network in the first application we compare the amplitude of data from vertical short period sensors to that of data from co located strong motion sensors and measure the amplitude calibration factors for 93 short period sensors among them 49 stations are measured at 1 0 42 measured at 0 6 as well as two outlying stations gff at 0 3 and chi at 1 3 these values are found to be related to the sensors sensitivity values in the second application we measure orientation discrepancy between 222 co located broadband and strong motion sensors all the vertical orientation differences are found to be within 5 however the horizontal orientation differences of 22 stations are greater than 6 among which four stations have reverse rotation or 180 from the expected orientation these measurements have been communicated to network operators and fixes are being applied this study together with our previously developed data monitoring framework demonstrates that comparison of different co located sensors is a simple and effective tool for a broad range of seismic data assessment and instrument calibration

polycyclic scoria cones of the antofagasta de la sierra basin southern puna plateau argentina fil baez walter ariel consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet salta instituto de investigaciones en energia no convencional universidad nacional de salta facultad de ciencias exactas departamento de fisica instituto de investigaciones en energia no convencional argentina

eruptive history of la poruna scoria cone central andes northern chile new stratigraphic lithological and petrographic analyses of la poruna scoria cone 21 53 s 68 30 w central andes northern chile allow the reconstruction of the eruptive sequence of this monogenetic cone petrographic and lithological characteristics allow us to identify three main lithostratigraphic units at la poruna scoria cone the first unit consists of agglutinated lapilli spatter beds and clastogenic lavas that are related to the construction of the cone the other two units are associated with a lava flow field and consist of flow of andesitic composition which differ both in their degree of weathering and in their development of channel surface and internal structures e g levees ogives and joints with these lithostratigraphic analyses we interpret that the construction of la poruna occurred during four main eruption phases involving strombolian hawaiian and transitional eruptive styles furthermore differences in the degree of erosion alteration and weathering of the lithostratigraphic units in the lava field of la poruna suggest that this flow field was formed during two eruptive events the excellent outcrop conditions and preservation state of the volcanic products of la poruna allow new stratigraphic insights that advance the wider and more general understanding and the dynamics of this important type of volcanism and the potential hazards of a scoria cone eruption the polycyclic style of the eruption needs to be included in the hazards assessment of these centers type especially when the cone is associated with structures that can be reactivated this process could correspond to a second phase of activity involving ash fall bomb and lava emission

geomorphology morphometry spatial distribution and ages of mafic monogenetic volcanoes of the peinado and incahuasi fields southernmost central volcanic zone of the andes abstract the back arc southern puna region south of 24 s in the central volcanic zone of the andes contains hundreds of miocene to quaternary mafic monogenetic volcanoes roughly distributed in several volcanic fields analysis of the geomorphology morphometry spatial distribution and age of 36 mafic monogenetic centers in the peinado and incahuasi fields at the southwestern margin of the puna plateau gives insights on the links that mafic monogenetic volcanism can have with main and secondary structures and the effects of degradation on scoria cone shape degree of preservation morphometry and six new unspiked k ar ages indicate two distinct age groups old centers 2 ma and young centers 1 ma the older mafic centers consist of degraded scoria cones and lava flows with an estimated cumulative bulk volume of 2 2 km3 the younger mafic centers display a variety of well preserved landforms scoria cones lava flows maars tuff rings domes and have an estimated cumulative volume of 6 2 km3 their distribution in a main nne ssw and secondary ene wsw trends suggests a control by the regional nne ssw striking peinado and san francisco fault systems in a dextral strike slip configuration scoria cone and lava flow morphometries are similar in both fields but a marked difference indicating hydrovolcanic activity is the presence of tuff rings maars and tephra fallout deposits only in the peinado field morphometric analysis of dated pristine and degraded scoria cones of the southern puna region shows that parameters related to crater depth and inner crater steepness decrease consistently with age suggesting that crater infilling is the degradation related process that is most sensitive to age at scoria cones in the southern puna high values of crater depth crater width crater depth cone height and mean inner crater slope are indicative of a young 1 ma age as young cones can have initially low values

shallowing and steepening subduction zones continental lithospheric loss magmatism and crustal flow under the central andean altiplano puna plateau

geomorphology and spatial distribution of monogenetic volcanoes in the southern puna plateau nw argentina abstract monogenetic volcanoes are the most common volcanic landforms on earth several works have shown that the study of geomorphology and spatial distribution of such small volcanoes reveals important aspects related to the volcanic field from eruption dynamics to tectonic processes the altiplano puna plateau 15 to 27 s central andes comprises the largest non collisional plateau on earth characterized by intensive deformation uplift and volcanism this region is marked by the presence of hundreds of mafic monogenetic volcanoes despite its discrete occurrence the monogenetic volcanoes show a close relationship with large scale lithospheric foundering events in the region in this contribution we applied a geographic information system gis approach in order to build the first complete catalog of monogenetic landforms present in the southern puna plateau 24 30 to 27 00 s nw argentina exploring their evolution and relationship with geotectonic events combining spatial analysis with a geomorphological study of each volcano it was possible to identify the presence of 285 monogenetic volcanoes in the region which could be grouped in seven clusters southern puna shows a predominance of cinder cones and lava domes suggesting a small influence of water in the eruption dynamics despite its high clustering degree southern puna monogenetic vents present a low density 8 3 10 3 vents km2 when compared to other monogenetic fields around the world in addition puna plateau cones show a close relationship with monogenetic cones associated with an extensional environment considering their back arc context based on relative and available absolute ages it was possible to map the volcanism evolution through time the results indicate that the first monogenetic volcanoes appeared in the central region of the plateau sierra de calalaste mainly associated with large scale nne ssw reactivated faults the activity then expanded antofalla and antofagasta regions and finally reached the borders of the plateau pasto ventura and arizaro regions which show volcanoes associated with nw se normal faults

moment tensor resolvability application to southwest iberia abstract we present a method to assess the uncertainty of earthquake focal mechanisms based on the standard theory of linear inverse problems we compute the uncertainty of the moment tensor m then map it into uncertainties of the strike dip and rake the inputs are source and station locations crustal model frequency band of interest and an estimate of data error the output is a six dimensional 6d error ellipsoid which shows the uncertainty of the individual parameters of m we focus on the double couple dc part of m the method is applicable both with and without waveforms the latter is particularly useful for network design as an example we present maps of dc resolvability for earthquakes in southwest europe computed without waveforms we find that the resolvability depends critically on frequency range and source depth shallow dc sources 10 km are theoretically better resolved than deeper sources 40 km and 60 km the dc resolvability of a 40 km deep event improves considerably when the portuguese network is supplemented by stations in spain and morocco the dc resolvability can be further improved by using a few ocean bottom seismometer obs stations or a dense land network a dense land network is able to resolve m well in spite of the large azimuthal gap which spans 200 the theoretical resolution analysis also explains the success of single station inversions when using a broad frequency range as exemplified by an application using waveforms of a m w 6 earthquake offshore iberia

fracture control on type morphology and distribution of parasitic volcanic cones an example from mt etna italy abstract this paper uses a coupled morphometric and stratigraphic analysis of several tens of parasitic pyroclastic cones of the se flank of mt etna volcano italy to explain the structure of a poorly understood actively deforming zone of the volcano moreover we present a new general classification of pyroclastic cones based on the parameterisation of coeval eruption points along the same magma feeding fracture each cone has been studied in detail in order to define its stratigraphic position morphometric characteristics growth evolution in relation to fracture distribution and orientation stress field and morphology of the substratum end members of this classification are at one side a simple circular or elongated edifice that grew around a single eruption point and can be related to a magma feeding fracture constrained by a relatively high confining stress in the substratum or a low magma pressure the other end member is a multiple rifted strongly elongated cone formed along multiple eruption points of a magma feeding fracture constrained by a relatively low confining stress or a high magma pressure lithostratigraphic and historical analyses demonstrate that the cones in this area developed between 15 ka bp and historical times the most recent one in 1669 ad testifying to a high rate of lateral eruption occurrence in the area these cones show n s elongated maximum crater axes n s trending axis of the depressed points of the crater rim and southward and southeastward breaching directions while coeval cones are n s aligned these morphometric characteristics reflect the geometry of n s magma feeding fractures the area can be regarded as a transitional weakness zone between the n s rift and the releasing system represented by the transtensional trecastagni and mascalucia faults indicating an e w oriented local component of extension possibly related to the interplay between the regional timpe fault system and the eastward gravitational spreading of the volcano the azimuth of breaching is controlled by magma feeding fracture orientation and substrate morphology especially in the eastern part of the area where it is influenced by the scarps related to the timpe regional fault system but it is also sensitive to cone development

determining the orientations of ocean bottom seismometers using ambient noise correlation 1 the cross correlation of multicomponent ambient seismic noise can reveal both the velocity and polarization of surface waves propagating between pairs of stations we explore this property to develop a novel method for determining the horizontal orientation of ocean bottom seismometers obs by analyzing the polarization of rayleigh waves retrieved from ambient noise cross correlation we demonstrate that the sensor orientations can be estimated through maximizing the correlation between the radial vertical component and the phase shifted vertical vertical component of the empirical green s tensor we apply this new method to the elsc eastern lau spreading center obs experiment data set and illustrate its robustness by comparing the obtained orientations with results from a conventional method utilizing teleseismic p and rayleigh wave polarizations when applied to a large obs array the ambient noise method provides a larger number of orientation estimates and better azimuthal coverage than typically is possible with traditional methods

compositional evolution of magma from paricutin volcano mexico the tephra record the birth of paricutin volcano mexico in 1943 provides an unprecedented opportunity to document the development of a monogenetic cinder cone and its associated lava flows and tephra blanket three type sections provide a complete tephra record for the eruption which is placed in a temporal framework by comparing both bulk tephra and olivine phenocryst compositions to dated samples of lava and tephra our data support the hypothesis of luhr 2001 that the first four months of activity were fed by a magma batch phase 1 that was distinct from the magma that supplied the subsequent eight years of activity we further suggest that the earliest erupted vanguard magma records evidence of temporary residence at shallow levels prior to eruption suggesting early development of a dike and sill complex beneath the vent depletion of this early batch led to diminished eruptive activity in june and july of 1943 while arrival of the second magma batch phase 2 reinvigorated activity in late july phase 2 fed explosive activity from mid 1943 through 1946 although most of the tephra was deposited by the end of 1945 phase 3 of the eruption began in mid 1947 with rapid evolution of magma compositions from basaltic andesite to andesite and dominance of lava effusion the combined physical and chemical characteristics of the erupted material present a new interpretation of the physical conditions that led to compositional evolution of the magma we believe that syn eruptive assimilation of wall rock in a shallow complex of dikes and sills is more likely than pre eruptive assimilation within a large magma chamber as previously assumed we further suggest that waning rates of magma supply from the deep feeder system allowed evolved shallowly stored magma to enter the conduit in 1947 thus triggering the rapid observed change in the erupted magma composition this physical model predicts that assimilation should be observable in other monogenetic eruptions particularly those with low pressure melt inclusions and with eruption durations of months to years

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

submerged coral reefs in the gulf of carpentaria australia abstract we report the discovery of three submerged living patch coral reefs covering 80 km 2 in the southern gulf of carpentaria australia an area previously thought not to contain coral bioherms the patch reefs have their upper surfaces at a mean water depth of 28 6 0 5 m and were consequently not detected by satellites or aerial photographs the reefs were only recognised in our survey using multibeam swath sonar supplemented with seabed sampling and under water video their existence points to an earlier late quaternary phase of framework reef growth probably under cooler climate and lower sea level conditions than today submerged reefs with surfaces between 20 and 30 m water depth occur in other regions of the earth and existing bathymetry indicates they could be widespread in the gulf many tropical regions that today do not support patch or barrier reefs for reasons similar to the modern gulf may have done so in the past when environmental conditions were more suitable submerged reefs may provide an important refuge for corals during the next few decades when near surface reefs are threatened by widespread coral bleaching due to warmer global sea surface temperatures

old cinder cone or young composite volcano the nature of cerro negro nicaragua determining whether a volcano is a cinder cone or a composite volcano is important because its classification categorizes the magmatic system and associated volcanic hazards the criteria of age and size of the volcano that are usually used for this assessment are inadequate for active young volcanoes other criteria on which that determination can be based are magma production rates cone morphology and eruption style cerro negro is an active young small basaltic volcano in northwestern nicaragua that is similar to both cinder cones and composite volcanoes in many ways it has had at least 22 historically documented eruptions since it first appeared in 1850 the most recent occurred in late 1995 the magma production rate for cerro negro 1 6 km 3 k y is of the same magnitude as those of a variety of composite volcanoes and an order of magnitude higher than the production rate for the paricutin cinder cone region of the trans mexican volcanic belt structurally cerro negro9s cone is a composite of scoria and lavas cut by dikes around a dense volcanic core cerro negro9s shape has been more like a composite volcano than a cinder cone except when infrequent sub plinian eruptions have altered the cone to make it look like a cinder cone comparisons of cerro negro to well known historically active cinder cones and young composite volcanoes show that it is best described as a young composite volcano the future hazards posed by cerro negro are therefore not those associated with cinder cone eruptions but the potentially more dangerous ones of composite volcanoes

syn eruptive morphometric variability of monogenetic scoria cones according to wood s model morphometric parameters such as slope angle can provide valuable information about the age of conical volcanic edifices such as scoria cones assuming that their initial slopes range from 30 to 33 measured manually on topographic maps and assuming that their inner architectures are homogenous this study examines the morphometric variability of nine young a few thousand years old small volume scoria cones from tenerife canary islands using high resolution digital elevation models in order to assess their slope angle variability because of the young age and minimal development of gullies on the flanks their morphometric variability can be interpreted as the result of syn eruptive processes including 1 pre eruptive surface inclination 2 vent migration and lava outflow with associated crater breaching and 3 diversity of pyroclastic rocks accumulated in the flanks of these volcanic edifices results show that slope angles for flank sectors differ by up to 12 among the studied volcanoes which formed over the same period of time this range greatly exceeds the 2 3 indicated by wood the greater than expected original slope range suggests that use of morphometric data in terms of morphometry based relative dating and detection of erosional processes and settings must be done with great care or detailed knowledge about absolute ages and eruption history especially in field scale morphometric investigation

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

a model for calculating eruptive volumes for monogenetic volcanoes implication for the quaternary auckland volcanic field new zealand abstract monogenetic basaltic volcanism is characterised by a complex array of behaviours in the spatial distribution of magma output and also temporal variability in magma flux and eruptive frequency investigating this in detail is hindered by the difficulty in evaluating ages of volcanic events as well as volumes erupted in each volcano eruptive volumes are an important input parameter for volcanic hazard assessment and may control eruptive scenarios especially transitions between explosive and effusive behaviour and the length of eruptions erosion superposition and lack of exposure limit the accuracy of volume determination even for very young volcanoes in this study a systematic volume estimation model is developed and applied to the auckland volcanic field in new zealand in this model a basaltic monogenetic volcano is categorised in six parts subsurface portions of volcanoes such as diatremes beneath phreatomagmatic volcanoes or crater infills are approximated by geometrical considerations based on exposed analogue volcanoes positive volcanic landforms such as scoria spatter cones tephras rings and lava flow were defined by using a light detection and ranging lidar survey based digital surface model dsm finally the distal tephra associated with explosive eruptions was approximated using published relationships that relate original crater size to ejecta volumes considering only those parts with high reliability the overall magma output converted to dense rock equivalent for the post 250 ka active auckland volcanic field in new zealand is a minimum of 1 704 km3 this is made up of 1 329 km3 in lava flows 0 067 km3 in phreatomagmatic crater lava infills 0 090 km3 within tephra tuff rings 0 112 km3 inside crater lava infills and 0 104 km3 within scoria cones using the minimum eruptive volumes the spatial and temporal magma fluxes are estimated at 0 005 km3 km2 and 0 007 km3 ka the temporal volumetric evolution of auckland is characterised by an increasing magma flux in the last 40 ky which is inferred to be triggered by plate tectonics processes e g increased asthenospheric shearing and backarc spreading of underneath the auckland region

an evaporation driven salinity maximum zone in australian tropical estuaries abstract the distribution of temperature and salinity in three tropical australian estuaries was measured in october 1983 in the hot dry season as a result of evaporation a salinity maximum zone exists near the mouth of the river where downwelling occurs and a classical and an inverse internal estuarine circulation prevail respectively upstream and downstream of the salinity maximum zone the zone of salinity maximum can be thought of as a high salinity plug inhibiting so much the mixing of estuarine and ocean waters that in some cases freshwater dose not reach the ocean

shear wave velocity and radial anisotropy structures beneath the central pacific from surface wave analysis of obs records abstract the central pacific plate is an ideal area to study the dynamics of the lithosphere asthenosphere system as this region is far away from other dynamics systems such as subduction zones and volcanic hotspots of mantle plumes and has experienced simple oceanic evolution in this study we collect three component continuous seismic data and differential pressure gauge data recorded by 15 broadband ocean bottom seismometers obss from the nomelt experiment we process continuous seismic noise data to obtain phase velocities of the fundamental 6 30 s and first high 5 11 s mode rayleigh waves and fundamental mode love waves 5 12 s we apply a two plane wave method to teleseismic rayleigh waves to obtain the fundamental mode phase velocities at 20 150 s periods and apply high resolution linear radon transform to teleseismic love waves to obtain phase velocities for the fundamental mode love waves at 28 48 s periods then we jointly invert the average phase velocities of rayleigh and love waves to construct 1 d isotropic shear wave velocity and radial anisotropy from the seafloor to 150 km depth beneath the nomelt region our 1 d model shows a low velocity zone lvz beneath a high velocity lid by comparing our results with the predictions of partial melt models we suggest the lvz is attributed to the presence of a small amount of melt in the asthenosphere strong radial anisotropy 5 6 is observed in the crust but the mantle lithosphere is characterized by weak radial anisotropy

clast size controls and longevity of pleistocene desert pavements at lathrop wells and red cone volcanoes southern nevada formation of desert pavement and accretionary soils are intimately linked in arid environments well sorted fallout scoria lapilli at lathrop wells 75 80 ka and red cone ca 1 ma volcanoes southern nevada formed an excellent parent material for pavement allowing infiltration of eolian silt and fine sand that first clogged the pore space of underlying tephra and then aggraded and developed vesicular a av horizons variations in original pyroclast sizes provide insight into minimum and maximum clast sizes that promote pavement and soil formation pavement becomes ineffective when clasts can saltate under the strongest winds while clasts larger than coarse lapilli are unable to form an interlocking pavement that promotes silt accumulation necessary for av development contrary to predictions that all pavements above altitudes of 400 m would have been reset in their development after late pleistocene vegetation advances the soils and pavements show clear differences in maturity between the two volcanoes this indicates that either the pavements and or soils develop slowly over many tens of thousands of years and then are very stable or if they are disrupted by vegetation advances subsequent pavements are re established with successively more mature characteristics

the calama olacapato el toro fault system in the puna plateau central andes geodynamic implications and stratovolcanoes emplacement abstract the structural evolution of the puna plateau is characterized by the activity of both orogen parallel and orogen oblique faults understanding the possible relationship between these two structural styles their geodynamic implications and the influence on the migration of magmas is important to get insights into the tectonic and magmatic evolution of the central andes in this study we present a structural analysis of the orogen oblique calama olacapato el toro fault system and the surrounding orogen parallel thrust faults in the central eastern puna plateau morphostructural analysis and field mapping reveal the geometry kinematics and dynamics of the tectonic features in the studied area we propose a three dimensional geometrical reconstruction of the main fault planes showing their attitude and intersections at depth the study indicates that the crust underwent simultaneous deformation along both the vertical transcurrent calama olacapato el toro fault system and the low angle thrust faults and that the back arc portion of the calama olacapato el toro fault system developed as a transfer zone among the main n striking thrusts our model considers that both orogen parallel and orogen oblique fault systems should be regarded as parts of the same tectonic system accommodating crustal shortening of a thickened crust the study suggests that the tectonic control on the magma and fluid circulation in the crust is mainly related to the geometry of the fault planes and the orientation of the stress field with a previously unrecognized important role played by the orogen parallel thrust faults on the emplacement of the stratovolcanoes

3 d crustal structure of the western united states application of rayleigh wave ellipticity extracted from noise cross correlations we present a new 3 d seismic model of the western united states crust derived from a joint inversion of rayleigh wave phase velocity and ellipticity measurements using periods from 8 to 100 s improved constraints on upper crustal structure result from use of short period rayleigh wave ellipticity or rayleigh wave h v horizontal to vertical amplitude ratios measurements determined using multicomponent ambient noise cross correlations to retain the amplitude ratio information between vertical and horizontal components for each station we perform daily noise pre processing temporal normalization and spectrum whitening simultaneously for all three components for each station pair amplitude measurements between cross correlations of different components radial radial radial vertical vertical radial and vertical vertical are then used to determine the rayleigh wave h v ratios at the two station locations we use all earthscope usarray tranportable array data available between 2007 january and 2011 june to determine the rayleigh wave h v ratios and their uncertainties at all station locations and construct new rayleigh wave h v ratio maps in the western united states between periods of 8 and 24 s combined with previous longer period earthquake rayleigh wave h v ratio measurements and rayleigh wave phase velocity measurements from both ambient noise and earthquakes we invert for a new 3 d crustal and upper mantle model in the western united states correlation between the inverted model and known geological features at all depths suggests good resolution in five crustal layers use of short period rayleigh wave h v ratio measurements based on noise cross correlation enables resolution of distinct near surface features such as the columbia river basalt flows which overlie a thick sedimentary basin

the rheology of crystal bearing basaltic magmas from stromboli and etna abstract our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics persistent activity displayed by basaltic volcanic systems such as etna and stromboli is governed mainly by the textural evolution and rheological properties of eruptive products here we investigate the high temperature 1131 c

the environmental significance of ventifacts a critical review abstract ventifacts wind abraded clasts or rock surfaces are common features of many terrestrial hot and cold deserts coastal periglacial and mountain environments as well as on mars and have a long history of investigation this review paper discusses some of the main themes in terrestrial ventifact research including their formation and geomorphic controls the varied morphological forms of ventifacts in terrestrial environments and their environmental significance as indicators of past and present wind direction and sediment mobility are critically evaluated future research directions are identified

recent slow normal and strike slip faulting in the pasto ventura region of the southern puna plateau nw argentina 1 recent normal and strike slip faulting on the puna plateau of nw argentina has been linked to lithospheric foundering gravitational spreading plate boundary forces and a decrease in crustal shortening from north to south however the timing kinematics and rate of extension remain poorly constrained we focus on the pasto ventura region nw argentina located on the southern puna plateau and recent deformation 1 ma field mapping and kinematic analysis across offset volcanic cinder cones show that the overall extension direction is subhorizontal is oriented ne sw to nne ssw and occurs at a slow time integrated rate of 0 02 to 0 08 mm yr since at least 0 8 0 5 ma a regional compilation from this study and existing data shows that recent extension across the puna plateau is subhorizontal but varies in azimuthal orientation dramatically data from the pasto ventura region are consistent with a number of models to explain normal and strike slip faulting on the puna plateau all of which likely influence the region some role for lower lithospheric foundering through dripping appears to be seen based on the regional extension directions and ages of mafic volcanism in the southern puna plateau

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

morphometric and morphological development of holocene cinder cones a field and remote sensing study in the tolbachik volcanic field kamchatka article i nfo the evolution of landscape over time is a central aspect of geological paleogeographical and geomorphological studies volcanic features like cinder cones offer the opportunity to monitor the processes and development of the landscape cinder cones are perhaps the simplest and most common volcanic landforms in the world morphological and morphometric study of cinder cones has proven an efficient tool for determining their relative dates and the erosional processes affecting them the extensive kamchatka volcanic province russian far east with its large tolbachik cinder cone field is an excellent case study for spatial and temporal classification and calibration of changes in morphometric values with time we show how the morphological and morphometric values of the monogenetic cinder cones measured in the field and by digital elevation models can be used to validate their age and erosional processes field data were gps measurements of cinder cones formed at the tolbachik 1975 1976 eruption and of holocene cinder cones erosion processes on the cinder cones and lava flows were identified and evaluated for every studied cinder cone morphometric parameters were assessed on the basis of remotely sensed data and digital elevation model morphometric measurements were taken of cone height and slope and average axis diameter and the height width ratio was obtained the comparison of morphometric parameters calculated from aster dem and topographic map clearly supports the concept of relative morphometric dating as the most recent cinder cones are always associated with the highest slopes and h w ratio the measured morphometric values of the recent tolbachik cinder cones are valuable benchmark data for determining erosion rates such as the measured values for the paricutin cone in mexico after the 1943 eruption the variability of the morphometric values of the recent cinder cones is due to their lithological coarse composition a comparison with the older cinder cones in the area shows that the climatic conditions of the kamchatka peninsula and the slow development of vegetation cover determine a high rate of erosion and rapid change in the morphometric values as compared to published values for other volcanic fields

interaction of ascending magma with pre existing crustal fractures in monogenetic basaltic volcanism an experimental approach 1 magma transport through dikes is a major component of the development of monogenetic volcanic fields these volcanic fields are characterized by numerous volcanic centers each typically resulting from a single eruption therefore magma must be transported from source to surface at different places which raises the question of the relative importance of 1 the self propagation of magma through pristine rock and 2 the control exerted by pre existing fractures to address this issue we have carried out a series of analogue experiments to constrain the interaction of a propagating dike through a medium with pre existing fractures the experiments involved the injection of air into an elastic gelatin solid which was previously cut into its upper part to simulate pre existing fractures the volume of the dikes their distance from the fractures and the ambient stress field were systematically varied to assess their influence on potential dike fracture interactions the results show that distance and angle between dikes and fractures influence these interactions and the dike trajectory dike geometry and dynamics are also affected by both the presence of the fractures and the dike volume dikes propagating in between fractures tend to decelerate in nature interactions are expected for dikes and fractures separated by less than about 200m and dikes with a volume less than about 10 2 km 3 would experience a velocity decrease these results highlight the influence of pre existing fractures on the mechanics and dynamics of dikes these heterogeneities must be considered when studying the transport of magmas within the crust

traveltime measurements from noise correlation stability and detection of instrumental time shifts we test the feasibility of using green s functions extracted from records of ambient seismic noise to monitor temporal changes in the earth crust properties by repeated measurements at regional distances we use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in california the correlations are computed in a moving 1 month window and we analyse the temporal evolution of measured interstation traveltimes the comparison of the arrival times in the positive and negative correlation time of rayleigh and love waves allows us to separate time shifts associated with any form of physical change in the medium those resulting from clock drift or other instrumental errors and those due to change in the localization of the noise sources this separation is based on the principle of time symmetry when possible we perform our analysis in two different period bands 5 10 and 10 20 s the results indicate that significant instrumental time errors 0 5 s are present in the data these time shifts can be measured and tested by closure relation and finally corrected independently of any velocity model the traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise between 1999 and 2005 the final arrival time fluctuations have a variance of the order of 0 01 s this allows us to measure interstation traveltimes with errors smaller than 0 3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period this level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in california such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes

late miocene early pliocene onset of n s extension along the southern margin of the central andean puna plateau evidence from magmatic geochronological and structural observations abstract extensional faulting typifies many of the earth s cenozoic orogenic plateaus the altiplano puna plateau in the southern central andes is the world s second largest orogenic plateau it contains a rich array of extensional fractures and normal faults with closely associated mafic volcanic flows dykes and cones this is in stark contrast to the foreland areas which record protracted shortening and continuous eastward growth of the mountain belt within the puna area a kinematic change over from shortening to extension has previously been inferred to have occurred during the quaternary however our research in the southern puna together with earlier petrologic investigations in the south central part of the plateau indicates an earlier onset for the extensional tectonism our analysis has focused on the eastern portion of the cordillera de san buenaventura in the southernmost part of the plateau where we mapped two upper miocene pliocene volcanic units associated with extensional faulting the aguada alumbrera ignimbrite and the la hoyada volcanic complex the structural inventory of these units records n s extensional deformation in the puna associated with the development of e w oriented fractures dykes normal and strike slip faults and folds new 40ar 39ar dating of magmatic rocks together with their relationships with the mapped structures reveal that widespread extension in the southern puna had already commenced by 5 ma and possibly as early as 7 ma although the extensional structures on the puna are typically associated with mafic volcanism the upper miocene pliocene la hoyada volcanic complex hosts dykes of intermediate compositions mafic to intermediate magmatism and extensional tectonism in this region is thus contemporaneous with and structurally akin to that in the central and northern parts of the plateau the ubiquitous cogenetic relationship between mafic volcanism and extensional tectonism both within the puna plateau and along its eastern flanks clearly indicates that the normal faulting is a regional phenomenon that is broadly coeval with an inferred rapid and large scale uplift of the altiplano puna plateau and a decrease in plate convergence rates these observations are compatible with a mantle delamination scenario in which the delamination of lithospheric mantle may have produced an ensuing weakening of the crust and regional uplift which may in turn have generated the conditions necessary to trigger gravitational extensional collapse beginning in the late miocene to early pliocene

the relations between faulting and mafic magmatism in the altiplano puna plateau central andes mafic lava flows and scoria cone on the altiplano puna plateau correlate spatially and temporalily with late pliocene quternary strike slip faulting thrust faulting dominated deformation in the plateau and adjacent foreland during the miocene pliocene the relations between faulting and mafic magmatism may be explained by a change from vertical to horizontal least principal compression during the pliocene quaternary a model in which mantle derived mafic magma ascends through the thick less dense continental crust of the altiplano puna plateau suggests that nonlithostatic stress in the crust may have controlled the depth and geometry of intrusion horizontal nonlithostatic compression favored the formation of horizontal mafic intrusions in the lower crust which may have thermally weakened the crust localized crustal thickening and caused crustal anatexis horizontal nonlithostatic tension favored vertical intrusions in the crust and surface eruption

a sinuous tumulus over an active lava tube at klauea volcano evolution analogs and hazard forecasts abstract inflation of narrow tube fed basaltic lava flows tens of meters across such as those confined by topography can be focused predominantly along the roof of a lava tube this can lead to the development of an unusually long tumulus its shape matching the sinuosity of the underlying lava tube such a situation occurred during k lauea volcano s hawai i usa ongoing east rift zone eruption on a lava tube active from july through november 2010 short lived breakouts from the tube buried the flanks of the sinuous ridge like tumulus while the tumulus crest its surface composed of lava formed very early in the flow s emplacement history remained poised above the surrounding younger flows at least several of these breakouts resulted in irrecoverable uplift of the tube roof confined sections of the prehistoric carrizozo and mccartys flows new mexico usa display similar sinuous ridge like features with comparable surface age relationships we contend that these distinct features formed in a fashion equivalent to that of the sinuous tumulus that formed at k lauea in 2010 moreover these sinuous tumuli may be analogs for some sinuous ridges evident in orbital images of the tharsis volcanic province on mars the short lived breakouts from the sinuous tumulus at k lauea were caused by surges in discharge through the lava tube in response to cycles of deflation and inflation di events at k lauea s summit the correlation between di events and subsequent breakouts aided in lava flow forecasting breakouts from the sinuous tumulus advanced repeatedly toward the sparsely populated kalapana gardens subdivision destroying two homes and threatening others hazard assessments including flow occurrence and advance forecasts were relayed regularly to the hawai i county civil defense to aid their lava flow hazard mitigation efforts while this lava tube was active

degradation of quaternary cinder cones in the cima volcanic field mojave desert california basaltic cinder cones in the cima volcanic field record a detailed history of progressive erosion in the arid environment of the eastern mojave desert these cones range in age from 0 015 m y to 1 09 0 08 m y as dated by radiocarbon or k ar analyses of the youngest lava flows from each cone cone heights range from 50 to 155 m and basal widths range from 400 to 915 m on younger cones height width ratios average 0 17 and crater width cone width ratios average 0 42 the degradational morphology of these cones displays several trends that are closely related to cone age 1 crater width cone width ratios decrease from 0 48 on the youngest cone to 0 21 on the oldest cone with a preserved crater 2 mean maximum side slopes tan sc decrease from 0 575 on the youngest cone to an average of 0 41 on the oldest cones studied 3 debris apron height cone height ratios increase from 0 10 on the youngest cone to an average of 0 34 on the oldest cones 4 cone drainage evolves from irregularly spaced rills and gullies on the youngest cone to regularly spaced gullies on 0 20 to 0 35 m y old cones to valleys as much as 110 m wide and 10 m deep on cones 0 59 m y old and older these trends form the basis of an empirical model of cinder cone degradation in arid environments this model documents 1 an erosional loss of 15 of cone volume during the first million years 2 progressive decline of cone slope at an average rate of 0 006 103 yr and cone height at an average rate of 2 25 cm 103 yr 3 initial rapid stripping of the loose cinder mantle from upper cone slopes accompanied by rapid debris apron formation and 4 a gradual transition between 0 25 and 0 6 m y from relatively uniform stripping of upper slopes to localized fluvial dissection of both cone slopes and debris apron this transition is apparently controlled by a concomitant change from diffuse subsurface drainage within the pervious cinder mantle to concentrated surface flow across the heterogeneous assemblage of agglutinate layers dikes and ponded flows of the cone interior

crustal radial anisotropy beneath the dabie orogenic belt from ambient noise tomography summary in this study we continue our previous work of imaging isotropic shear velocity to study the crustal radial anisotropy beneath the dabie orogen and surrounding regions by jointly analysing rayleigh wave and love wave dispersion curves in addition to processing the vertical component data to retrieve rayleigh waves we collect horizontal component continuous ambient noise data and retrieve love waves from cross correlations of horizontal component noise data between station pairs then we measure love phase velocity dispersion curves at periods from 8 to 35 s using a spectral method and perform surface wave tomography to obtain high resolution phase velocity maps finally we determine crustal radial anisotropy by inverting the local phase velocity dispersion curves of rayleigh and love waves our model of crustal radial anisotropy reveals complex anisotropic patterns associated with the dynamic processes of continent continent collisions and post collision reworking between the north china craton and the yangtze craton in the huabei basin the radial anisotropy is positive throughout the entire crust corresponding to areas with extensional tectonics developed since the middle mesozoic in the jianghan basin strong positive radial anisotropy in the middle and lower crust is observed most likely resulting from subhorizontal alignment of seismic anisotropic materials under the crustal extensional deformation in the eastern dabie orogenic belt the radial anisotropy beneath northern dabie complex ndc appears positive in the upper and lower crust and negative in the middle crust the positive radial anisotropy in the upper crust is probably because of the presence of igneous rocks with anisotropic minerals aligned subhorizontally under the action of the extensional tectonics during igneous extrusion and emplacement whereas the positive radial anisotropy in the lower crust is probably because that subhorizontal alignment of anisotropic materials induced by magmatic underplating formed after the delamination of the orogeny in the middle crust finite strains associated with the vertical intrusion of deep magma might cause crystalline anisotropic minerals aligned vertically resulting in observed negative radial anisotropy in the western dabie orogenic belt positive radial anisotropy is present in the whole crust except beneath the hong an ultrahigh pressure uhp area where radial anisotropy is negative in the middle crust similar to ndc the hong an uhp probably experienced similar thermal geodynamic processes as the eastern dabie and the negative radial anisotropy might be also the result of vertical alignment of anisotropic minerals caused by the vertical intrusion of deep magma strong localized negative radial anisotropy in the middle crust beneath the xinyang area is imaged most likely caused by the vertical alignment of anisotropic minerals crystallized from the vertically intruding mafic magma originated from the upper mantle during the volcanism

the madinah eruption saudi arabia magma mixing and simultaneous extrusion of three basaltic chemical types during a 52 day eruption in 1256 a d 0 5 km3 of alkali olivine basalt was extruded from a 2 25 km long fissure at the north end of the harrat rahat lava field saudi arabia the eruption produced 6 scoria cones and a lava flow 23 km long that approached the ancient and holy city of madinah to within 8 km three chemical types of basalt are defined by data point clusters on variation diagrams i e the low k high k and hybrid types all three erupted simultaneously their distribution is delineated in both scoria cones and lava flow units from detailed mapping and a petrochemical study of 135 samples six flow units defined by distinct flow fronts represent extrusive pulses the high k type erupted during all six pulses the low k type during the first three and the hybrid type during the first two

the structure of the crust and uppermost mantle beneath south china from ambient noise and earthquake tomography summary two years of continuous recordings of ambient seismic noise observed at 354 stations in south china from 2009 to 2010 are used to estimate rayleigh wave group and phase velocity maps from 6 to 40 s period these results are merged with rayleigh wave phase velocity maps from 25 to 70 s period derived from earthquakes in the same time frame eikonal tomography generates the dispersion maps which by monte carlo inversion are used to estimate a 3 d vsv model of the crust and upper mantle down to a depth of 150 km across all of south china with attendant uncertainties a clear image emerges of the west yangtze block a region of the western yangtze craton characterized by relatively thick crust 40 km overlying a seismic mantle lithosphere that extends to at least 150 km that may have been the nucleus for the formation of the yangtze craton in the archean and may present a present day obstacle to the eastward expansion of tibet the west yangtze block contrasts with the thinner crust 30 km and mantle lithosphere 70 80 km beneath the eastern yangtze craton and south china foldbelt these observed differences are consistent with processes associated with flat slab subduction in the mesozoic that may have eroded the lithosphere of the eastern yangtze craton and the south china foldbelt

what drives centuries long polygenetic scoria cone activity at barren island volcano abstract barren island in the andaman sea is an active mafic stratovolcano which had explosive and effusive eruptions followed by caldera formation in prehistoric time poorly dated a scoria cone within the caldera marking volcanic resurgence was active periodically from 1787 to 1832 the historic eruptions since 1991 the same scoria cone has produced six eruptions commonly including lava flows links between barren island s eruptions and giant earthquakes such as the 26 december 2004 great sumatra megathrust earthquake have been suggested though there is no general correlation between them the 227 year long activity of the scoria cone named here shanku cone is normally driven by purely magmatic processes i present a source to surface model for barren island and shanku including the source region deeper and shallow magma chambers volcanotectonics dyking from magma chambers and eruptions and eruptive style as controlled by crustal stresses composition and volatile content calculations show that dykes 0 5 m thick and a few hundred meters long originating from shallow level magma chambers 5 km deep are suitable feeders of the shanku eruptions shanku a polygenetic scoria cone at least 13 eruptions since 1787 has three excellent analogues namely anak krakatau 40 eruptions since 1927 cerro negro 23 eruptions since 1850 and yasur persistent activity for the past hundreds of years this is an important category of volcanoes gradational between small monogenetic scoria cones and larger polygenetic volcanoes

three dimensional crustal structures of the shanxi rift constructed by rayleigh wave dispersion curves and ellipticity implication for sedimentation intraplate volcanism and seismicity

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere

upper mantle anisotropy from long period p polarization we introduce a method to infer upper mantle azimuthal anisotropy from the polarization i e the direction of particle motion of teleseismic long period p onsets the horizontal polarization of the initial p particle motion can deviate by 10 from the great circle azimuth from station to source despite a high degree of linearity of motion recent global isotropic three dimensional mantle models predict effects that are an order of magnitude smaller than our observations stations within regional distances of each other show consistent azimuthal deviation patterns while the deviations seem to be independent of source depth and near source structure we demonstrate that despite this receiver side spatial coherence our polarization data cannot be fit by a large scale joint inversion for whole mantle structure however they can be reproduced by azimuthal anisotropy in the upper mantle and crust modeling with an anisotropic reflectivity code provides bounds on the magnitude and depth range of the anisotropy manifested in our data our method senses anisotropy within one wavelength 250 km under the receiver we compare our inferred fast directions of anisotropy to those obtained from pn travel times and sks splitting the results of the comparison are consistent with azimuthal anisotropy situated in the uppermost mantle with sks results deviating from pn and ppol in some regions with probable additional deeper anisotropy generally our fast directions are consistent with anisotropic alignment due to lithospheric deformation in tectonically active regions and to absolute plate motion in shield areas our data provide valuable additional constraints in regions where discrepancies between results from different methods exist since the effect we observe is local rather than cumulative as in the case of travel time anisotropy and shear wave splitting additionally our measurements allow us to identify stations with incorrectly oriented horizontal components