spatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands ii deception island images this work has been partially supported by the spanish project ephestos cgl2011 29499 c02 01 by the eu project ec fp7 mediterranean supersite volcanoes med suv by the basque government researcher training program bfi09 277 and by the regional project grupo de investigaci on en geof isica y sismolog ia de la junta de andaluc ia rnm104 edoardo del pezzo was partly supported by dpc ingv projects unrest speed and v2 precursori

array analysis of seismograms from explosive sources evidence for surface waves scattered at the main topographical features in this article we analyze the seismic wavefield produced by blasts fired at mt vesuvius for a deep seismic sounding experiment and recorded by a dense short period three component seismic array seismograms from five explosions occurring at the bottom of wells located at different distances and azimuth with respect to the array site have been analyzed with the zero lag cross correlation technique applied to both vertical and horizontal components in the frequency range 3 7 hz the aim is to analyze the portion of the seismograms long after the first p onset in order to obtain the slowness and backazimuth distribution of correlated secondary phases polarization analysis in time domain carried out using the array covariance matrix technique has also been applied to the well correlated phases to determine their wave composition results show that the correlated phases detected in the coda of the seismogram shots are composed almost entirely of surface waves location of the scatterers shows a high concentration of the scatterers in and around the volcanic edifice of mt vesuvius confirming that topographical irregularities play an important role in the generation of the high frequency scattering phenomena

zircon u pb age hf isotopes and geochemistry of shuichang algoma type banded iron formation north china craton constraints on the ore forming age and tectonic setting abstract the shuichang iron deposit is an algoma type bif in the north china craton the shuichang bif is interlayered with plagioclase hornblende gneiss indicating that these two lithologies are temporally closely associated we use the content of major elements and their ratios in order to define the protolith of the plagioclase hornblende gneiss sims u pb dating of zircons from the plagioclase hornblende gneiss suggests that the shuichang bif was formed at ca 2547 7 ma and was subjected to metamorphism at 2513 4 ma the major elements and ree data of the ore as well as individual magnetite and chert bands indicate that the shuichang bif precipitated from hydrothermal fluids discharging on the sea floor and that iron and silica may be associated with submarine volcanic activity in situ lu hf analysis of zircons from the plagioclase hornblende gneiss yielded initial 176 hf 177 hf ratios from 0 280903 to 0 281197 and e hf t values from 10 5 to 0 4 with a weighted mean value of 8 72 0 38 the single stage hf model age ranges from 2836 ma to 3249 ma we infer that the protolith of the plagioclase hornblende gneiss originated from the enriched mantle mixed with a small amount of subducted crust materials the shuichang bif formed at 2 5 ga and is coeval with other bifs in north china and in other cratons in the world we propose that the shuichang bif was formed in a subduction related back arc basin or intra arc basin based on the geochemical signatures of the wall rocks we further point out that the 2 5 ga global bif formation peak not only predates the amalgamation of the north china craton but probably also record an ancient supercontinent event

array analyses of seismic noise at mt vesuvius volcano italy abstract the properties of the seimic noise wavefield at mt vesuvius volcano italy are investigated using a dense array of short period seismometers deployed on the south west flank of the volcano and operated on 1997 1998 the array had an aperture of 500 m and average station spacing of 40 m the main goal of this deployment was to investigate the possible presence of correlated signals which could be attributed to subsurface magmatic and or hydrothermal activity volcanic tremor the spectral properties of the noise wavefield are investigated using data from the arrays and from the summit stations of the permanent seismic network operated by the vesuvius observatory the seismic noise is characterized by three main spectral peaks at frequencies

time dependent spatial amplitude patterns of harmonic tremor at arenal volcano costa rica seismic wave interferences seismograms recorded at the receivers of a small aperture seismic array usually display very similar waveforms and amplitudes as a consequence of their close proximity during the analysis of the volcanic tremor wave field at arenal volcano costa rica we detected significant differences in the amplitudes of harmonic tremor recorded at the stations of a small aperture 210 m seismic array the amplitude distributions are geometrically complex and characterized by strong gradients they occur just for harmonic tremors any other type of seismic event produces nearly uniform amplitudes across the array this suggests some relation with harmonic frequency content moreover the spatial amplitude patterns change with time some of these observations could be explained by an extreme combination of source path and site effects but they also could be produced by interference of different components of the seismic wave field we use numerical calculations to investigate the amplitude pattern generated by two interfering plane waves and are able to reproduce the main features of the observed amplitude patterns we propose mechanisms that might generate seismic wave fields with multiple components and conclude that interference can explain the complexity and variability of the harmonic tremor wave field at arenal volcano online material wave field animation

two stage collision related extrusion of the western dabie hp uhp metamorphic terranes central china evidence from quartz c axis fabrics and structures abstract the western dabie orogen also known as the hong an block forms the western part of the dabie sulu hp uhp belt central china rocks of this orogen have been subjected to pervasive ductile deformation and include numerous quartz schists and felsic mylonites cropping out in ductile shear zones quartz textures in these mylonites contain important clues for understanding the movement sense of late collisional extrusion and exhumation of high pressure ultrahigh pressure hp uhp rocks from the lower crustal level to the upper crustal level during middle triassic and early jurassic the orientation and distribution of quartz crystallographic axes were used to confirm the regional shear sense across the orogen the asymmetry of c axis patterns consistently indicates top to the southeast thrusting across the orogen in early structural stages later stages of deformation show different senses of movement in northern and southern parts of the orogen with top to the northwest sinistral shearing recorded in rocks north of the xinxian hp uhp eclogite facies belt and top to the southeast dextral shearing south of the same unit based on our study on quartz c axis fabrics and marco to micro scale structures simultaneous southeastward shearing within a large part of the orogen and normal faulting north of the xinxian hp uhp unit is explained by upward extrusion in early stages of deformation the extrusion process has been attributed to syn and late collisional processes accounting for some earlier deformation in the western dabie orogen such as metamorphic sequences around the core of the xinxian hp uhp eclogite facies unit much higher pressure of deformation is also indicated in the aligned glaucophane and omphacite from blueschist and eclogite in the field an orogen parallel eastward extrusion of the xinxian hp uhp eclogite facies unit however occurred diachronously in later stages of deformation therefore a tectonic model combining an early upward extrusion with a later eastward extrusion is presented two different stages and types of extrusion for exhumation of hp uhp rocks are suitable to all of east central china geochronological data shows that the first upward extrusion occurred during middle triassic the second eastward extrusion occurred during late triassic to early jurassic these two extrusions are correlative with two stages of rapid exhumation of the dabie hp uhp rocks respectively these two stage late collisional middle triassic to early jurassic extrusion events bridge the gap between syn collisional early to middle triassic vertical extrusion and post collisional cretaceous eastward directed lateral escape and provide vital clues to understanding the more detailed processes of exhumation of hp uhp rocks

high frequency site effects at two parkfield downhole and surface stations abstract using stacked ratios of microearthquake source spectra recorded at the surface and 200 m downhole we have established the p and s wave site effect at two locations in parkfield california the frequency responses of both sites are bimodal being completely dominated by multiples and amplification below 10 hz and by attenuation above 30 hz the low frequency amplification factors show roughly three to five times more uphole motion compared to that downhole the multiples produce peaks with a maximum of nearly 10 times more uphole motion above 50 hz the downhole motion is always larger approaching a factor of 5 at the high frequency limits of our study when fit with a linear attenuation model the high frequency ratios yield compressional and shear q values between 6 and 19 the data were divided into subsets based on event location and time of year statistical comparison of these subsets shows no systematic variation with azimuth or season the results of our study accounts for the lack of high frequency surface reflections in the parkfield downhole data but not for the lack of source scaling of parkfield microearthquakes

tectonic systems and the deposition of iron formation abstract the iron formation group of chemically precipitated cherty iron rich sediments ranges in age from early precambrian to recent and is composed of a variety of lithological facies iron formations are classified as lake superior and algoma types to emphasize the contrasting conditions in the spectrum of sedimentary tectonic environments in which they formed thick stratigraphic units of lake superior type iron formation which form the most extensive iron ranges of the world are part of sedimentary tectonic systems that developed along the margins of cratons or continental platforms and were deposited over extended periods of time under relatively stable tectonic conditions the algoma type iron formations were deposited with volcanic rocks and greywacke in various tectonic volcanic systems formed under more dynamic tectonic conditions but are otherwise comparable to present day spreading ridges on the ocean floor the thick sequences of lake superior type iron formation deposited between 2 7 and 2 0 ga form part of major sedimentary tectonic systems that extended along the margins of continents direct biogenic factors and the composition of the atmosphere probably had only limited influence on the precipitation of these chemical sediments

near surface scattering effects observed with a high frequency phased array at pinyon flats california analysis of data collected by a high frequency array experiment con ducted at pinyon flat in southern california provides strong evidence that the high frequency wave field from local earthquakes at this hard rock site are strongly dis totted by near surface scattering the seismic array we deployed consisted of 60 2 hz natural frequency three component sensors deployed in a three dimensional array two of the sensors were located in boreholes at 150 and 275 m depth the other 58 sensors were deployed in an areal array above these boreholes thirty six of these were deployed in a 6 by 6 element grid array with a nominal spacing of 7 m centered over the borehole sensors the remaining 22 seismometers were laid out in two 11 element linear arrays radiating outward from the grid coherence calculations reveal a rapid loss of coherence at frequencies over 15 hz at all but the shortest length scales of this array three dimensional visualization techniques were used to closely examine the spatial stability of particle motions of p and s waves this reveals systematic variations of particle motion across the array in which the particle motion tracks tilt drastically away from the backazimuth expected for an isotropic medium these variations however are frequency dependent below around 8 hz the particle motions become virtually identical for all stations at progressively higher frequen cies the wave field particle motion becomes increasingly chaotic frequency wave number analysis of these data provide quantitative measures of the same phenomena we find that direct wave f k spectra are bathed in a background of signal generated noise that varies from 10 to 30 db down from the direct arrival signal this signal generated noise appears to be nearly white in wavenumber indicating the wavelength of this noise on the scale of tens of meters and less refraction measurements we made on two lines crisscrossing the array reveal that the weathered layer velocities are highly variable and define a very strong wave guide measured surface p wave velocities varied from 400 to 1300 rn sec and velocities at depth of approximately 15 m varied from 1600 to 2700 m sec previous measurements in the boreholes showed that the intact granite below about 65 m depth has a velocity of approximately 5400 m sec these results demonstrate the extreme velocity contrast and degree of velocity heterogeneity of the near surface at this site we conclude that all the ob servations we made can be explained by strong scattering of incident body wave signals into a complex mishmash of body wave and surface wave modes in this heterogeneous near surface wave guide

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

coda waves a review the analysis and interpretation of coda waves have received increasing attention since the early seventies in the past few years interest in this subject has spread worldwide and the study of high frequency seismic coda waves has become a very important seismological topic as a conclusion of the studies accomplished in this time coda waves are considered the result of scattering processes caused by heterogeneities acting on seismic waves p ands waves play a particularly important role in this interaction the process introduces an attenuation which added to the intrinsic absorption gives the observed apparent attenuation therefore coda waves constitute a thumbprint left by the heterogeneities on the seismograms coda waves offer decisive information about the mechanism of how scattering and attenuation take place this review describes coda waves in detail and summarizes the work done in this subject to 1986 the relation between coda waves and attenuation in the context of research on seismic scattering problems is stressed particular attention has been given to the application of coda waves to estimate source and medium parameters the state of the art of the temporal variations of coda wave shape and the possible use of these variations as an earthquake precursor also are presented care has been taken to introduce the statistical models used to deal with the heterogeneities responsible for scattering

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

shallow velocity structure and seismic site effects at arenal volcano costa rica abstract we use the spatial autocorrelation spac method with improved inversion algorithms to estimate the love and rayleigh dispersion curves at two sites at the west and northeast flanks of arenal volcano costa rica at the west flank site the rayleigh waves phase velocities vary from 765 m s 1 at 1 hz to 300 m s 1 at 12 hz and those of love waves between 780 and 295 m s 1 in the same frequency band at the northeast flank site the rayleigh wave velocities range from 1386 to 300 m s 1 and those of love from 1983 to 315 m s 1 from dispersion curves we derive shallow strong variations in amplitude of the spectral peaks are observed for the seismic events along two radial arrays these site effects are analysed using the h v spectral ratio method and s wave theoretical transfer functions results show that the wave amplifications are related to resonance effects of shallow structure when a resonance of the shallow layers occurs the correlation coefficients between close stations increase at the corresponding frequency the site effects may thus produce spurious results with the spac method the h v spectral ratio used in complement of the spac method can help detecting the site effects and testing the plane layer hypothesis furthermore the theoretical transfer functions calculated for the estimated velocity models is also useful to validate the models

the application of zircon cathodoluminescence imaging th u pb chemistry and u pb ages in interpreting discrete magmatic and high grade metamorphic events in the north china craton at the archean proterozoic boundary abstract two distinct late neoarchean to early paleoproterozoic magmatic events are recognized at the northern margin of the eastern block of the north china craton based on interpretation of zircon structure cathodoluminescence signature th u pb chemistry and age the first event is represented by emplacement of the chaihe trondhjemite and xianjinchang tonalite with magmatic zircon core ages ranging from 2559 2553 7 ma respectively these rocks experienced a subsequent high grade metamorphic event constrained by partial recrystallization of primary magmatic zircon and growth of new zircon rims between 2517 and 2490 ma a second magmatic episode generated by partial melting of crustal rocks during this metamorphic event is represented by the hongshilazi syenogranite with an age of 2502 11 ma the short time interval between initial magmatism and high grade regional metamorphism signifies they were related to the same major tectonothermal event when considered along with evidence of a similar sequence of events at this time 800 km to the south in eastern hebei and the previously established 2500 ma age of granulite facies metamorphism in mafic rocks across the craton it is proposed that a large mantle plume developed beneath the north china craton at the close of the archean

a mantle derived bimodal suite in the hercynian belt nd isotope and trace element evidence for a subduction related rift origin of the late devonian brevenne metavolcanics massif central france in the brevenne series ne massif central a low grade bimodal association of metabasalts and metarhyolites is exposed together with intrusive trondhjemite bodies zircon u pb dating constrains their magmatic emplacement at 366 5 ma and 358 1 ma respectively the metabasalts are characterized by a distinct enrichment in incompatible elements e g th and lree and positive ndi from 5 to 8 combined isotope and trace element systematics rule out crustal contamination of mafic melts as a suitable cause of the lile large ion lithophile element enrichment rather a mixing process between a component similar to mid ocean ridge basalts and an enriched end member with ndi 5 is suggested an enriched mantle source of ocean island basalt affinity is precluded by the relative depletion of high field strength elements especially nb which shows negative anomalies in chondrite normalized patterns on the contrary a subduction related origin for the lile enrichment would be more consistent it may be inferred that arc like melts enriched in th and lree light rare earth elements and depleted in nb with ndi 5 were produced through partial melting of a depleted mantle source to which a small amount of crustally derived component had been added the metarhyolites are enriched in lile and have a close genetic relationship with the metabasalts as evidenced by their high ndi from 4 7 to 6 8 although the chemical evidence remains ambiguous it is suggested that fractional crystallization accompanied by subordinate assimilation is the petrogenetic process most consistent with the data the trondhjemites are isotopically distinct from the metarhyolites their ndi values from 1 0 to 2 2 reflect an important contribution of continental crust to their genesis and disprove their inferred cogenetism with the felsic volcanics a review of modern environments in which such bimodal suites are exposed shows that settings involving incipient rifting of a volcanic arc fringing a continental margin or built upon young thin continental crust might provide suitable analogues geodynamic reconstructions are complicated by subsequent tectonic events which disrupted the initial patterns and by mesozoic cenozoic sedimentary cover however this subduction related magmatism enlarges the growing body of evidence for southward subduction processes until the late devonian during the evolution of the northern flank of the european variscides as a general implication it is suggested that the combined use of the sm nd system with incompatible elements relatively resistant during alteration and low grade metamorphism ree th zr nb may provide diagnostic criteria for recognizing the tectonic setting of bimodal metaigneous suites in ancient orogenic belts

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

seismic signals associated with landslides and with a tsunami at stromboli volcano italy in this article we analyze the seismic signals produced by two landslides that occurred at the stromboli volcano on 30 december 2002 recorded by both broadband and short period seismic stations located in the 2 5 22 km distance range from the source for both landslides the characteristics of the low frequency seismograms indicate a complex time history in the release of seismic energy the first landslide occurred over the submerged part of the northwest sector of the volcano and had associated a large amplitude low frequency pulse representative of the abrupt detachment of a large mass lower amplitude phases in the following 3 minutes possibly indicate minor detachment events the highest amplitude low frequency signals are well described by a single force source model the second mass failure episode is also characterized by a complex source and can be interpreted as a multiple event with a less abrupt onset and at least four detachments occurring during 4 5 minutes and producing low frequency signals synthetic seismograms generated by a shallow single force located in the submerged area of sciara del fuoco and directed upslope fit well the first low frequency seismic pulse recorded at stromboli and panarea by three component stations from this simulation we estimated the force exerted by the first mass failure the estimate of the volume through two different procedures gives values in the range of 1 0 1 5 million m3 and about 14 million m3 respectively the landslides which involved both the submarine and the subaerial northwest flank of the volcano produced a tsunami that struck the coast of stromboli island and in a few minutes reached the other islands of the aeolian archipelago three broadband seismic stations installed on land about 100 m from the coastline at panarea island located 20 km southwest of stromboli recorded very long period seismic signals produced by the tsunami waves analysis of these signals gives invaluable information on the spectral content and propagation properties of tsunami waves and on their interaction with the ground at a short distance from the coast synthetic tsunami waves obtained by a landslide source model and taking into account the bathymetry of the sea surrounding stromboli and panarea islands fit the observed phenomena and the experimental data very well manuscript received 19 november 2003

coda wave imaging of the long valley caldera using a spatial stacking technique numerous geological and seismological studies of the long valley caldera eastern california suggest that it is at present an active magmatic system tomographic measurements utilising local and regional earthquake data have traditionally been made on the principle direct arrivals this paper presents the results from a technique developed to image the s wave attenuation structure we measure the attenuation value of the s wave coda from almost 17 000 vertical component seismograms a more stable estimate of q is determined from coda waves which are less sensitive to local path effects than direct waves as they sample a volume we find that the resultant tomograms produced from spatial stacking show a high attenuation anomaly qs 125 centred within the caldera compared with qs 220 outside the caldera

observations of loma prieta aftershocks from a dense array in sunnyvale california a small aperture 300 m four station array was deployed in sunnyvale california for 5 days to record aftershocks of the loma prieta earthquake of october 1989 the purpose of the array was to study the seismic response of the alluvium filled santa clara valley and the role of surface waves in the seismic shaking of sedimentary basins strong motion records of the loma prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the santa clara valley we use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3 6 and 4 4 apparent velocities are generally observed to decrease with increasing time after the s wave in the seismograms phases arriving less than about 8 sec after the s wave have apparent velocities comparable to the s wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces for times 10 to 30 sec after the direct s wave we observe long period 1 to 6 sec arrivals with apparent velocities decreasing from 2 5 to 0 8 km sec we interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records much of the energy in the 40 sec after the s wave is coming approximately from the direction of the source although some arrivals have backazimuths as much as 60 different from the backazimuths to the epicenters two of the aftershocks show arrivals coming from 30 to 40 more easterly than the epicenters this energy may have been scattered from outcrops along the southeastern edge of the basin in contrast the deepest aftershock studied d 17 km displays later arrivals with backazimuths 30 to 40 more westerly than the epicenter a distinct arrival for one of the aftershocks propagates from the southwest possibly scattered from the western edge of the basin synthetic seismograms derived from a plane layered crustal model do not produce the long period love waves observed in the waveforms of the ml 4 4 aftershock these love waves may be generated by the conversion of incident s waves or rayleigh waves near the edge of the basin

precise determination of the relative wave propagation parameters of similar events using a small aperture seismic array 1 we propose a method to determine accurately the relative wave propagation parameters apparent slowness and propagation azimuth of a cluster of seismic events with similar waveforms recorded on a seismic array this relative slowness estimate relse method is based on precise measurements of the delays among arrivals of different earthquakes to each of the array receivers delays are determined using interpolations of the cross correlation functions of the earthquake waveforms accurate relative slowness vectors are estimated using a least squares fit of the observed delays to the delays corresponding to the arrivals of plane wave fronts we tested the method using both synthetics and real data in order to understand its resolution capabilities in presence of seismic noise and to assess the uncertainty regions associated with the slowness vector estimates from these analyses we establish a procedure to determine the 90 uncertainty regions associated with the estimates of relative slowness vectors as an example of application of the relse method we analyzed a multiplet composed of 16 similar earthquakes recorded during the 1999 seismic crisis at deception island volcano antarctica using a conventional slowness estimate method produces virtually the same result for every earthquake because of the large uncertainties alternatively using the relse method reduces the uncertainties of the estimates and allows to resolve the detailed distribution of relative apparent slowness vectors our results show that the slowness vectors are aligned within a narrow north south trending band which represents a clue toward the features of the source region and or source distribution we repeated the procedure using different earthquakes as master events the estimated distribution of slowness vectors is similar in every case which demonstrates that our results are independent of the choice of reference event index terms 7299 seismology general or miscellaneous 7203 seismology body wave propagation 7215 seismology earthquake parameters 7230 seismology seismicity and seismotectonics 7280 seismology volcano seismology 8419 keywords seismic arrays slowness vectors multiplet analysis deception island volcano

the first second of volcanic eruptions from the erebus volcano lava lake antarctica energies pressures seismology and infrasound 1 we describe a multiparameter experiment at erebus volcano antarctica employing doppler radar video acoustic and seismic observations to estimate the detailed energy budget of large up to 40 m diameter bubble bursts from a persistent phonolite lava lake these explosions are readily studied from the crater rim at ranges of less than 500 m and present an ideal opportunity to constrain the dynamics and mechanism of magmatic bubble bursts that can drive strombolian and hawaiian eruptions we estimate the energy budget of the first second of a typical erebus explosion as a function of time and energy type we constrain gas pressures and forces using an analytic model for the expansion of a gas bubble above a conduit that incorporates conduit geometry and magma and gas parameters the model consistent with video and radar observations invokes a spherical bulging surface with a base diameter equal to that of the lava lake the model has no ad hoc free parameters and geometrical calculations predict zenith height velocity and acceleration during shell expansion during explosions the energy contained in hot overpressured gas bubbles is freed and partitioned into other energy types where by far the greatest nonthermal energy component is the kinetic and gravitational potential energy of the accelerated magma shell 10 9 j seismic source energy created by explosions is estimated from radar measurements and is consistent with source energy determined from seismic observations for the generation of the infrasonic signal a dual mechanism incorporating a terminally disrupted slug is proposed which clarifies previous models and provides good fits to observed infrasonic pressures a new and straightforward method is presented for determining gas volumes from slug explosions at volcanoes from remote infrasound recordings

array analysis using circular wave front geometry an application to locate the nearby seismo volcanic source summary the zero lag cross correlation technique used for array analysis in the hypothesis of plane waves has been modified to allow the wave front to be circular synthetic tests have been performed to check the capability of the method which returns the input test data when the source array distances are not greater than two or three times the array aperture for this distance range the method furnishes an estimate of the apparent velocity and the epicentral coordinates of the source for more distant sources the method becomes equivalent to that based on the planar wave approximation which gives an estimate of the backazimuth to the source and the apparent velocity the method has been applied to seismic data recorded at the active volcano located at deception island antarctica 35 volcanic long period events occurring in a small swarm were selected results show that the epicentres are close to the array between 0 4 and 2 km and aligned in a sw direction in agreement with one of the main directions of the fracture system of deception volcano

3d scattering image of mt vesuvius in this article we apply a passive scattering imaging method derived from the method developed by nishigami 1991 to data from the coda of the local volcano tectonic vt earthquakes of mt vesuvius this method provides the space distribution of the strong scatterers together with a rough estimate of their strength in the development of our method we use a realistic raytracing calculated with a ray bending approach in the 3d velocity model of mt vesuvius structure obtained with travel time inversion the inversion procedure adopted for the scattering imaging in the present study is based on the conjugate gradient method cgm the volume under study is divided into cubic cells with different dimensions in a multiscale approach we obtain the best resolution 900 m cubic cell size in the central part of the volume under study roughly in a radius of 4 km centered in the crater within a depth of 5 km we analyzed the coda signals after filtering in two frequency bands the first centered at 12 hz and the second at 18 hz where most of the seismic energy is concentrated results show that most of the strong scatterers are located in the depth range between the surface and 3000 m below the sea level in correspondence with the crater axis where most of the seismicity occurs part of the scatterers are located in the zones characterized by the maximum velocity contrasts

detailed analysis of wave propagation beneath the campi flegrei caldera italy we investigate the complex propagation of seismic waves beneath the campi flegrei caldera italy using multichannel recordings of artificial explosions the sources consisted of air gun explosions shot in the gulf of pozzuoli at offsets ranging between 3 and 7 km a multichannel recording device was deployed in the solfatara crater and consisted of ten vertical component and two three component short period seismometers with a maximum aperture of about 150 m the zero lag correlation zlc technique was adopted to estimate horizontal slowness and backazimuth of coherent waves crossing the array for sources located in the northern sector of the gulf with maximum offset 5 km ray parameters and backazimuths are in agreement with those predicted for the 1d velocity model used for routine locations for sources at offsets larger than 5 km the zlc curves depict prominent maxima associated with a secondary phase propagating with a lower velocity than the first arrival p wave using finite difference synthetic seismograms generated for a 2d realistic velocity model we explain these late arrivals in terms of a lateral velocity variation located at depths of about 1 km such discontinuity would correspond to a positive vp anomaly imaged by a recent 3d tomographic study and interpreted as the submerged southern rim of campi flegrei caldera collapsed during the explosive eruption of 12 ky b p the small spacing among adjacent shot points allowed simultaneous wave field decomposition at the source and receiver arrays using a modified version of the double beam method we retrieve the independent variation of horizontal slowness at both the source and receiver regions for both cases we found azimuthal deviations as large as 50 with respect to the great circle path at the source region these discrepancies may be interpreted in terms of ray bending at the interface of the aforementioned positive anomaly at the receiver array the observed anomalies may be attributed to either velocity variations marking the solfatara crater rim or to a near receiver low velocity body whose position would coincide with negative gravimetric anomalies and a high vp vs ratio region inferred by independent geophysical and seismological studies

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

quantitative analysis of seismic wave propagation anomalies in azimuth and apparent slowness at deception island volcano antarctica using seismic arrays summary we analyse shot data recorded by eight seismic arrays during an active source seismic experiment carried out at deception island antarctica in 2005 january for each source we estimate the apparent slowness and propagation azimuth of the first wave arrival since both source and receiver positions are accurately known we are able to interpret the results in terms of the effect of the heterogeneities of the medium on wave propagation the results show the presence of significant propagation anomalies nearby shots produce large apparent slowness values above 0 6 s km 1 while distant shots produce small values down to about 0 15 0 20 s km 1 these values are different for each array which shows the importance of the local structure under the receiver the spatial distributions of apparent slowness are not radial as we would expect in a flat layered medium and again these distributions are different for each array the azimuth anomalies defined as the difference between the empirical estimates and the values expected in a 1 d model i e the source array directions suggest ubiquitous wave front distortions we have detected both positive and negative anomalies for some shot array geometries azimuth anomalies are quite large with values up to 60 the distribution of the anomalies depends on the position of the array some of these features can be interpreted in terms of a shallow magma chamber and shallow rigid bodies imaged by high resolution seismic tomography however several details remain unexplained further work is required including modelling of synthetic wavefields on realistic models of deception island and or apparent slowness vector tomography

collision leading to multiple stage large scale extrusion in the qinling orogen insights from the mianlue suture abstract the geologic framework of the phanerozoic qinling dabie orogen was built up through two major suturing events of three blocks from north to south these include the north china craton including the north qinling block the qinling dabie microblock and the south china craton including the bikou block separated by the shangdan and mianlue sutures the mianlue suture zone contains evidence for mesozoic extrusion tectonics in the form of major strike slip border faults surrounding basement blocks a late paleozoic ophiolite and a ca 240 200 ma thrust belt that reformed by 200 150 ma thrusts during a type intracontinental subduction the regional map pattern shows that the blocks are surrounded by complexly deformed devonian to early triassic metasandstones and metapelites forming a regional scale block in matrix melange fabric five distinct tectonic units have been recognized in the belt 1 basement blocks including two types of precambrian basement crystalline and transitional 2 continental margin slices including early paleozoic strata and late paleozoic fluviodeltaic sedimentary rocks proximal and distal fan clastics reflecting the development of a north facing rift margin on the edge of the south china plate 3 out of sequence oceanic crustal slices including strongly deformed postrift deep water sedimentary rocks sheeted dikes basalts and mafic ultramafic cumulates of a late paleozoic ophiolite suite developing independent of the rift margin in a separate basin 4 out of sequence island arc slices 5 accretionary wedge slices all the tectonic units were deformed during three geometrically distinct deformation episodes d 1 d 2 and d 3 during 240 200 ma units 2 4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the d 1 episode thrust slices 20 km south of the mianlue suture are related to this vertical extrusion due to the same rock assemblages ages and kinematics the d 2 and d 3 episodes folded all the units in a thick skinned style about east west d 2 and west northwest d 3 axes in the mianlue suture zone an early foreland propagating sequence of accretion of late paleozoic rocks deposited above the yangtze craton is not involved in d 1 deformation but is temporally equivalent to the d 2 and d 3 deformation in the mianlue suture two stages of strike slip faulting mainly occurred at the end of d 2 and d 3 respectively during d 2 deformation the bikou block was obliquely indented to the ese into the mianlue suture rather than being thrust over the mianlue suture from the north as a part of the qinling dabie microblock during d 3 deformation however the bikou block was bounded by the south boundary fault of the mianlue suture and the yangpingguan fault on the south these faults are coeval strike slip faults but of opposite senses and accommodated minor southwestward extrusion of the bikou block into songpan ganze orogen the other basement blocks north of the mianlue suture were extruded eastward by about 20 km of lateral displacement based on the offset of the wudang dome during the d 3 episode due to the northeastward indentation of the hannan complex of the south china craton post d 3 emplacement of granite cutting across the strike slip faults such as the mianlue suture provides a minimum age of 200 ma for d 3 deformation therefore based on insights from the evolution of the mianlue suture the d 2 and d 3 episodes in the mianlue suture and its neighbors are not responsible for and associated with the two stage extrusion of the dabie uhp hp terranes from the foping dome to the present erosional surface more than 350 km

array analysis of the seismic wavefield of long period events and volcanic tremor at arenal volcano costa rica we use wavefield decomposition methods time domain crosscorrelation and frequency domain music to analyze seismic data recorded by a dense small aperture array located 2 km west of arenal volcano costa rica and operated during 2 5 days the recorded wavefield is dominated by harmonic tremor and includes also spasmodic tremor and long period lp events we find that the initial stages of lp events are characterized by three different wave arrivals these arrivals propagate with similar back azimuths pointing to the volcano summit 80 n and increasing apparent slownesses of 0 4 1 1 and 1 7 s km spasmodic tremors can not be regarded as coherent signals on the contrary harmonic tremors are highly coherent characterized by the stability of the apparent slowness vector estimates apparent slownesses lay in the range 1 2 s km back azimuths point in the general direction of the volcano but with a large variability 40 120 n nevertheless there are long term variations and evidences of multiple simultaneous components in the harmonic tremor wavefield these observations suggest that lp events and tremor are generated in a shallow source area near the volcano summit although they do not share exactly the same source region or source processes the tremor source is located in the shallowest part of the plumbing system beneath the lava crust this dynamic region is subject to complex fluctuations of the physical conditions degassing events at different locations of this region might generate variable seismic radiation patterns the effects of topography and heterogeneous shallow structure of the volcano may amplify these variations and produce the wide directional span observed for volcanic tremor on the other hand the lp source seems to be more repeatable lp events are likely triggered by fragmentation of the fluid flow in a slightly deeper portion of the volcanic conduits

f k analysis of noress array and single station data to identify sources of near receiver and near source scattering abstract f k analyses of short period recordings of both u s and soviet underground nuclear explosions at the eskdalemuir eka scotland array indicate arrivals from a local source about 15 km due northwest of the array use of residual seismograms derived by subtracting the beamed record from each array channel confirmed the presence of the same scatterer the secondary seismic source appears to be short period surface waves due to the scattering of incident p waves at a nearby deep valley known as moffat water in agreement with key s 1967 earlier results similar analyses of the noress norway array data from u s and soviet nuclear shots also indicate secondary arrivals suggesting a local near surface scatterer about 25 30 km south west of the array in the region of lake mjosa thus short aperture array data can be useful in identifying and locating sources of near receiver scattering f k analyses of short period recordings of both explosion and earthquake sources at the high frequency noress array indicate secondary arrivals from a near receiver source about 25 30 km southwest of the array f k power difference plots obtained by subtracting after normalization the f k power versus slowness estimates for the initial p window from those for the later windows provided nearly identical results the secondary seismic source appears to be short period surface waves rg generated by the scattering of incident p waves in the region of lake mjosa 27 km sw of noress where there is about 1 km of relief from the bottom of the lake to the top of an adjacent hill

archean granulite gneisses from eastern hebei province china rare earth geochemistry and tectonic implications the granulite gneisses and their retrograded products of the qianxi group from eastern hebei province china have been investigated for their isotope and trace element geochemistry a consistent age of about 2 5 ae has been obtained by the rb sr and sm nd whole rock isochron methods in agreement with the zircon u pb data pidgeon 1980 d y liu unpubl geochemical arguments from initial isotopic ratios isr and ind and elemental distribution patterns have led us to conclude that this age of about 2 5 ae represents the time of granulite facies metamorphism which must have followed closely the primary emplacement of their protoliths previous claims for early archean ages 3 5 ae of these granulites are not substantiated the mineral isotope systematics register an important thermal event at about 1 7 ae roughly corresponding to the time of the widespread luliang orogeny ma and wu 1981 or chungtiao movement huang 1978

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

early paleozoic to devonian multiple accretionary model for the qilian shan nw china abstract the qilian shan located in the northern tibetan plateau of nw china has an excellent record of early to middle paleozoic subduction accretion that resulted from convergence between the alax and qaidam blocks but there is no consensus about its detailed tectonic history this paper summarizes its tectonic divisions and discusses its tectonic evolution from the cambrian to devonian the belt has the following tectonic divisions in the far north the southern passive margin of the alax block is juxtaposed against an early cambrian to ordovician marianan type intra oceanic arc north qilian the north qilian arc is separated from a japanese type arc central qilian to the south by a high pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts the central qilian is bounded to the south by a wide melange zone south qilian consisting of ophiolitic slices and continental margin sequences farther to the south lies the oulongbuluk microcontinent that is separated from the qaidam block and farther south by an ultrahigh pressure metamorphic belt tectonostratigraphic analysis together with geochemical geochronological and geophysical data indicates a complex evolution by subduction accretion processes from the cambrian to the devonian before final amalgamation and docking to the northern alax block this model solves the long lasting discussion on the polarity of subduction in paleozoic time this multiple subduction accretion history sheds light on the continuity of paleozoic sutures along the qilian shan and the nature of the altyn tagh fault and thus contributes to an improved understanding of the tectonic architecture of central asia

broadband f k analysis of array data to identify sources of local scattering f k analyses of short period recordings of both u s and soviet underground nuclear explosions at the eskdalemuir eka scotland array indicate arrivals from a local source about 15 km due northwest of the array use of residual seismograms derived by subtracting the beamed record from each array channel confirmed the presence of the same scatterer the secondary seismic source appears to be short period surface waves due to the scattering of incident p waves at a nearby deep valley known as moffat water in agreement with key s 1967 results similar analyses of the noress norway array data from u s and soviet nuclear shots also indicate secondary arrivals suggesting a local near surface scatterer about 25 30 km southwest of the array in the region of lake mjosa thus short aperture array data can be useful in identifying and locating sources of near receiver scattering

extreme crustal metamorphism during columbia supercontinent assembly evidence from north china craton abstract a vast supracrustal belt of khondalites granulite facies metapelites occur along the northern margin of the north china craton we report here for the first time spinel quartz equilibrium assemblage from these rocks in two textural settings 1 high zno up to 14 47 wt spinel with quartz as inclusions within garnet porphyroblasts defining pressure above 12 kbar and temperature of 900 c and 2 low zno down to 1 2 wt spinel in association with quartz in the matrix assemblage formed during peak ultrahigh temperature conditions ca 975 c and 9 kbar we present a unique case of decompression where the metamorphic conditions of the rocks traversed mostly through the spinel quartz extended stability field monazite grains in textural association with both types of spinel quartz textures were analysed for age determination and the data define two age peaks at 1927 11 ma and 1819 11 ma since the peak thermal regime of the khondalites was close to or exceeded the theoretical closure temperature of pb in monazite we infer the 1819 11 ma age as the timing of ultrahigh temperature event in this craton our data lend support to the idea of ca 1 9 1 8 ga e w collisional orogen at the northern margin of the north china craton we correlate the extreme crustal metamorphism with tectonics associated with the assembly of the north china craton within the columbia supercontinent

geophysical and geological tests of tectonic models of the north china craton abstract the geometry and timing of amalgamation of the north china craton have been controversial with three main models offering significantly different interpretations of regional structure geochronology and geological relationships one model suggests that the eastern and western blocks of the ncc formed separately in the archean and an active margin was developed on the eastern block between 2 5 and 1 85 ga when the two blocks collided above an east dipping subduction zone a second presumes the eastern block rifted from an unknown larger continent at circa 2 7 ga and experienced a collision with an arc perhaps attached to the western block above a west dipping subduction zone at 2 5 ga and the 1 85 ga metamorphism is related to a collision along the northern margin of the craton when the ncc joined the columbia supercontinent a third model suggests two collisions in the central orogenic belt at 2 1 and 1 88 ga but recognizes an early undated deformation event recent seismic results reveal details of the deep crustal and lithospheric structure that support both the second and third models showing that subduction beneath the central orogenic belt was west directed and that there is a second west dipping paleosubduction zone located to the east of the cob dipping beneath the western block ordos craton the boundaries identified through geophysics do not correlate with the boundaries of the trans north china orogen suggested in the first model and the subduction polarity is opposite that predicted by that model high pressure granulite facies metamorphism at 1 85 ga is not restricted to the tnco as suggested by the first model but is documented across the ncc as predicted by the second model suggesting a major continent continent collision along the north margin of the craton at 1 85 ga further it has recently been shown that in the southern tnco there is no record of metamorphism at circa 1 85 ga but only at 2 7 2 5 ga showing that the tnco as defined as a circa 1 85 ga orogen does not exist this is further confirmed by recent re os isotopic studies which show that the subcontinental lithospheric mantle beneath the southern cob is late archean in age and that a province in the northern ncc is circa 1 8 ga correlating with the proposed collision belt of the ncc with the columbia supercontinent across the entire ncc the cob is an archean convergent belt re worked in the paleoproterozoic and the paleoproterozoic tectonism is widespread across the ncc as predicted by the model whereby the previously amalgamated eastern and western blocks experienced a continental collision with columbia at circa 1 85 ga but uplift exhumation rates are slow necessitating a re evaluation of the tectonic models of the ncc

3d scattering image of the campi flegrei caldera southern italy new hints on the position of the old caldera rim abstract a scattering image of the campi flegrei caldera has been obtained using coda wave envelopes from local microearthquake data recorded at a portable 12 station digital network this was operated during the paroxysmic phase of the ground uplift bradyseism that occurred in the years 1983 1984 the nishigami technique has been used to obtain the 3d distribution of the strong scatterers in an earth volume with a horizontal extension of 20 km 20 km and a vertical thickness of 6 km this earth volume was segmented in blocks of 2 km 2 km 2 km for the outer section and in blocks of 1 km 1 km 1 km for the inner section the inversion was performed using a hybrid jackknife svd method that has allowed qualitative control of the stability and robustness of the solution the results show that the scatterers revealed by the coda envelopes which were band pass filtered at a center frequency of 18 hz match the inner border of the caldera rim which is well outlined on land by geological observations the scatterer position also delineates this border well beneath sea level these results are in close agreement with recently obtained seismic velocity tomography the scatterers imaged at the 6 and 12 hz band pass frequencies are located around the zone of maximum uplift beneath solfatara crater where most of the present residual volcanic activity is concentrated

imaging laterally varying regional heterogeneities from seismic coda using a source array analysis abstract seismic coda is composed of scattered waves originated from various kinds of heterogeneities whose locations are not confined in the great circle ray path direction between the source and receiver we devise a technique to image laterally varying regional heterogeneities using single station seismograms for clustered events we analyze regional seismic records of the borovoye seismic station for the balapan nuclear explosions in kazakhstan scattered waves that arrive coherently over the source arrays are extracted by directional beamformings the locations of scatterers responsible for the scattered waves are mapped from the beamforming direction travel time and slowness equivalently phase velocity the illuminated locations of heterogeneities are highly correlated with the structural variations in surface topography crustal thickness and sedimentary thickness the influence of the structural variations on seismic waves is quantified in terms of scattering intensity and quality factor the scattering properties are observed to vary with phase due to the difference in frequency content and phase velocity the proposed technique appears to be useful for a study of active tectonic regions with limited monitoring stations

response of flexible piles under laterally linear movement of the sliding layer in landslides observational results indicate that the lateral movement of the sliding layer in landslides is usually not uniform but approximately linear in this paper a subgrade reaction solution for the response of flexible piles in landslides is developed where the influence of the laterally linear movement of the sliding layer on the response of flexible piles in landslides is considered the study of case histories indicates that the calculated and measured responses of flexible piles in landslides compare well with each other dimensionless design charts are proposed based on the new subgrade reaction solution key words piles slope stabilization landslides soil pile interaction subgrade reaction solution

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

observations of high frequency scattered waves using dense arrays at teide volcano abstract a study of the seismic coda of seven small earthquakes recorded on the teide volcano canary islands spain was carried out using a temporary small aperture 12 station seismic array the purpose was to measure backazimuth apparent velocity and the type of waves that compose the coda in the frequency range 4 to 6 hz we used the zero lag cross correlation zlc method to obtain the components of the wave vector and three component analysis techniques based on the covariance matrix of the signal in the time domain to investigate the polarization properties of the signals the results show that a great part of the coda signals in the analyzed frequency range are almost uncorrelated while a low number of isolated correlated arrivals show an apparent slowness between 2 10 3 and 2 5 10 4 sec m and an almost random distribution of backazimuths the correlated arrivals have been interpreted as generated by strong scatterers probably related to the presence in the study area of surface topography irregularities the volcanic cone and the caldera rim the wave type varies from pure s type waves to mixed surface waves with some rayleigh components

the contribution of topographic scattering to teleseismic coda in southern california given that seismic coda is largely the result of scattering near the receiver a tie to geological complexity i e to crustal heterogeneity is expected but a systematic and predictive understanding of the important aspects of geology is lacking we have developed a technique for mapping the origins of coda energy as recorded by regional networks that provides insight into the proximal generation of seismic coda here the role of topography in the production of surface propagating coda energy both as a scatterer and as a proxy of shallow geologic structure is examined for the portion of the san andreas fault system within the southern california seismic network we find significant correlation of p to rg scattering potential with topographic roughness that extends to relatively subtle topography the correlation peaks at a migration velocity of 2 9 km s confirming the identification of scattered rg energy and offering an alternative means of estimating regional shallow velocity structure