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

reconstruction of megalake chad using shuttle radar topographic mission data in the 2 500 000 km2 lake chad basin in central africa the 2000 shuttle radar topographic mission srtm data have been used to supplement the existing topographic data srtm data produce much sharper images of the region s topography and provide new insights into debates about the nature and extent of late quaternary lake chad this paper shows that the accuracy of srtm30 the recently released 30 arc seconds topographic data from srtm largely surpasses that of previous global digital elevation models dems available in the region using a gis we identified from srtm30 elevation data key features in the landscape topography providing further evidence for the existence of a megalake chad the srtm30 data corroborate the presence of two ancient shorelines associated with stillstands of the paleolake at the elevation of the mayo kebbi and bahr el ghazal spillovers we found a general flattening of the topography in the region covered by megalake chad which is most likely the result of wave cut action the srtm30 data show that the remains of the highest paleoshoreline have a constant elevation of 325 5 m amsl at its maximum extent megalake chad had an area of about 340 000 km2 only 8 less than the present day world s largest lake the caspian sea the srtm30 data also revealed ancient drainage networks in the sahara that lead to megalake chad we compiled available 14c dates to constrain holocene megalake chad events the results presented in this paper have significant consequences for improving our knowledge of regional paleohydrology and continental climate change this study is also the first step for a gis based reconstruction of late quaternary paleohydrology in tropical africa

lapse time dependence of coda q anisotropic multiple scattering models and application to the pyrenees abstract the coda quality factor of short period s waves q c excited by local earthquakes in the pyrenees has been measured as a function of the length of the coda window l w for different choices of the onset time of the coda t w in the 2 16 hz frequency band we observe a transient regime characterized by an increase of q c with l w followed by a stabilization around a plateau the value of which depends on the central frequency of the signal using monte carlo simulations of wave transport in a variety of random media 1200 models we demonstrate that the lapse time dependence of q c in the pyrenees may be modeled by multiple anisotropic scattering of seismic waves without invoking any depth dependence of the attenuation properties in the crust in our model anisotropic scattering is quantified by the ratio between the transport mean free path and the mean path l l at 6 hz the data require an anisotropy factor l l 5 a transport mean free path l 400 km and an intrinsic quality factor q i 800 from the frequency dependent plateau of q c at large lapse time we infer an intrinsic quality factor of the form q i 400 f 0 4 in the pyrenees we also show how the rapid increase of the lapse time dependence of q c with frequency may be exploited to put constraints on the power spectrum of heterogeneities in the crust

measurements of intrinsic and scattering seismic attenuation in the crust intrinsic and scattering attenuation parameters qi and qs have been measured in three different tectonic areas for local and shallow earthquakes located close to the receiver the approach developed by wennerberg 1993 which takes into account the numerical correction of the coda q parameter for the multiple scattering formulation of zeng was used to infer from the estimates of coda q and direct s wave q the intrinsic qi and scattering qs q values results for 1 to 12 hz range show that qi is comparable to qs for the etna volcano and for the campi flegrei area while qi for the tectonically active area of granada is lower than qs coda q is close to intrinsic q suggesting that at least in the crust coda q is a good estimate of the intrinsic q volcanic areas show a reasonable higher degree of heterogeneity if compared with the nonvolcanic area of granada

intrinsic and scattering seismic wave attenuation in the central apennines italy abstract recently an earthquake sequence formed by a series of subsequences characterized by large earthquakes three events m 6 0 and five events m 5 0 occurred in the central apennines in 6 7 months during 2016 2017 several studies interpreted this cascading type of earthquake occurrence as associated with fluid movements through an interconnected network of cracks around the active faults that triggered the subsequences in different time and location in the present study we aim to verify if the presence of fluids is confirmed by the pattern of seismic wave attenuation to do so we separately estimate the space averaged parameters intrinsic qi 1 and scattering qs 1 proportional to the correspondent attenuation parameters by applying a modified multiple lapse time window analysis mltwa in order to establish reference background values for the study region mltwa measures the decay of s wave energy with distance and lapse time and fit it to the energy transport equation solution for scattering yielding the seismic albedo b0 qs 1 qt 1 and the extinction length le qt 1 parameters as a function of frequency the knowledge of the separated attenuation parameters allows determining which process of seismic energy dissipation dominates in the region in the present study b0 results to be around0 6 at 1 5 hz and decreases with increasing frequency down to 0 2 indicating that the attenuation of the seismic energy carried by s wave is controlled by intrinsic dissipation rather than by scattering moreover the intrinsic attenuation is frequency dependent f 0 9 for the uniform model and f 0 4 for the crust moho model this behavior well matches with the presence of fluids in the faults and fracture zones in the central apennines in agreement with results from other independent studies in the region finally a comparison among the attenuation parameters estimated for this area and those measured in several areas of italy and other parts of the world is presented together with a discussion on the comparison between the present mltwa attenuation estimates and homologous results obtained for the same area with different approaches

coda q distribution in the canary islands abstract the canary archipelago near the african plate between 27 and 30 n and 13 and 19 w is included in the oldest region 135 m y of the eastern atlantic ocean the tectonic seismicity is moderate with low magnitudes and it is almost totally related to an active fault located between the islands of tenerife and gran canaria the purpose of this paper is to provide a clear idea of the anelasticity of coda waves in the region in order to compute master dispersion curves as a function of the quality factor q we have applied inversion methods to obtain analytical magnification curves for all the seismographic stations used fp t data corresponding to the coda wave dispersion of 52 local and regional seismic events recorded at 6 seismographic stations have been obtained the fit of the data to the master curves determined yields estimates of coda q values and their frequency dependence most of the q0 values determined at 1 hz vary between 100 and 300 showing a strong frequency dependence in the range 0 2 2 hz the characteristic v value degree of frequency dependence of q in the region given by the law q q0 fv is v 0 9 by applying regionalization techniques an iso q0 map for a reference frequency of 1 hz has been obtained for the canary archipelago this map shows important lateral variations in q0 reflecting the tectonics and the volcanism of the region the lowest q0 values are found along the trend of the fault and beneath the islands

seismic codas on the earth and the moon a comparison the phenomenon of the seismic coda which is composed of seismic energy delayed by scattering is seen on both the earth and the moon on the moon the scattered coda is very large relative to body wave arrivals with a delay of the time of maximum energy whereas on earth scattered codas are relatively small and show no delay of the energy maximum in both cases the form of the coda is controlled by three distance scales the mean free path l which is the average distance seismic energy travels before it is scattered the attenuation distance x which is the average distance seismic energy travels before it is attenuated and the source receiver distance r two coda models are discussed based on these parameters a strong scattering diffusion model and a weak scattering single scattering model a discussion of the diffusion scattering model indicates that if x l 1 diffusion scattering is an appropriate model but if x l 1 single scattering is the appropriate model within the appropriate range of r a survey of the literature indicates that for the frequency range 0 5 10 hz diffusion scattering is important in lunar codas but for the frequency range 1 25 hz single scattering is important in terrestrial codas another important effect of attenuation is the elimination of scattering paths much longer than x on the moon this means that seismic energy in the coda can only propagate directly in the near surface strong scattering zone between surface sources and the seismometer for source seismometer separations of the order of x l 12 otherwise scattering is limited to regions near the source and the receiver on earth this effect probably prevents multiple scattering

magma supply path beneath mt asama volcano japan 1 obtaining a sharp image of magma supply path through dense geophysical observations is important for forecasting time and magnitude of hazardous future eruptions here we reveal a clear magma plumbing system using dense seismic and geodetic networks around mt asama central japan magma intrusions occurred several times beneath the western flank of mt asama forming a wnw ese directed zone with 1 km below sea level the eastern end of this zone connects a narrow vertical pathway extending right under the summit crater which erupted in 2004 monitoring magmatic activity with a well designed observational network is vital to mitigate future volcano hazards

sediment transport by dry ravel 1 dry ravel is a general term that describes the rolling bouncing and sliding of individual particles down a slope and is a dominant hillslope sediment transport process in steep arid and semiarid landscapes during fires particles can be mobilized by the collapse of sediment wedges that have accumulated behind vegetation on a daily basis particles may be mobilized by bioturbation and by small landslides experiments on a dry ravel flume indicate that a basic expression of the momentum equation predicts the distance traveled by particles propelled down a rough surface this equation is further elaborated to produce a nonlinear slope dependent transport equation for dry ravel that represents the rate at which sediment crosses a contour width of slope sediment traps installed on two hillslope transects near santa barbara california measured the flux from dry ravel initiated by bioturbation and the data support the form of the equation additionally a physical model based on the infinite slope stability analysis is proposed for the initiation of dry ravel by landsliding the analytical result from this model is supported by experiments and field data reported by others

late quaternary palaeoenvironments in the lake barombi mbo west cameroon deduced from pollen and carbon isotopes of organic matter abstract a sediment core 23 5 m long was recovered from a water depth of ca 110 m in lake barombi mbo a maar crater of the cameroon volcanic chain this paper presents a carbon isotopic curve of organic matter linked to the main results of the pollen analysis interpretation of this carbon isotopic curve is simplified 1 because of the weak role played by the phytoplankton in the balance of the organic particle flux and 2 because of the presumed absence of diagenetic alteration of the isotopic composition the carbon isotopic curve exhibits an almost linear correlation with that of total grass pollen which form the main part of the c4 biomass the major fluctuations of isotopic and pollen curves allow four main phases to be distinguished from ca 25 000 to 20 000 yr b p 13c values of 25 to 30 pdb are related to a forest environment associated with a montane floral element from 20 000 to 13 000 yr b p the 13c values are between 23 and 28 and are linked to openings of landscape with a mosaic of forest and savanna and a fall of lake level with colonization of the shores by cyperaceae and other aquatic plants from 13 000 to 10 000 yr b p the forest extended again reaching a maximum density during the period from 9500 until 3000 yr b p and with an average 13c value of 32 a new dry phase at around 2500 2000 yr b p with temporary openings in the forest marked by a 13c excursion above 30 but during the last 2 millennia the forest developed again with 13c values of 32

spatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands i model and the case of tenerife island 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 edp has been partly supported by dpc ingv projects unrest speed and v2 precursori

fluvial sediment transport in response to moderate storm flows following chaparral wildfire ventura county southern california chaparral wildfire has a profound effect on erosion and sedimentation in southern california the wheeler fire in july 1985 burned the entire basin of a tributary drainage area 2 14 km 2 of the north fork of matilija creek near ventura california after the fire fine gravel was delivered to the channel by the process of dry ravel dry particle by particle sliding of debris under the force of gravity at a rate of 0 29 m 3 km 2 month the first winter flow 2 1 m 3 s following the fire deposited 550 m 3 of fine gravel in the 270 m study reach near the mouth of the tributary at least 90 of this fine gravel was derived from colluvium delivered by dry ravel processes from hillslopes near the channel the second winter flow 2 5 m 3 s eroded the channel to the pre fire thalweg a reduction in particle size and critical shear stress associated with deposition of small gravel following the fire allowed these moderate magnitude flows to transport large volumes of sediment deposits of two debris flows were identified in the tributary basin radiocarbon dating of these deposits gives dates of 1045 95 yr b p for the older deposit and between 295 35 and 385 84 yr b p for the younger deposit these dates indicate that the recurrence interval of large debris flows in the study basin is at least an order of magnitude greater than the recurrence interval of fire in the area

a 3d discrete numerical elastic lattice method for seismic wave propagation in heterogeneous media with topography 1 a three dimensional elastic lattice method for the simulation of seismic waves is presented the model consists of particles arranged on a cubic lattice which interact through a central force term and a bond bending force particle disturbances are followed through space by numerically solving their equations of motion a vacuum free surface boundary condition is implicit in the method we demonstrate that a numerical implementation of the method is capable of modelling seismic wave propagation with complex topography this is achieved by comparing the scheme against a finite difference solution to the elastodynamic wave equation the results indicate that the scheme offers an alternative 3d method for modelling wave propagation in the presence of strong topography and subsurface heterogeneity we apply the method to seismic wave propagation on mount etna to illustrate its applicability in modelling a physical system

intrinsic and scattering attenuation images of usu volcano japan we present intrinsic and scattering q attenuation images for usu volcano japan by analyzing over 1800 vertical seismograms by fitting the observed envelopes to the diffusion model we obtained intrinsic and scattering attenuation values at three different frequency bands using a back projection method and assuming a gaussian type weighting function we obtained the 2d images of intrinsic and scattering attenuation resolution tests confirm the robustness and reliability of the obtained images we found that scattering attenuation is the dominant process of energy loss in the frequency range analyzed which suggests strong spatial heterogeneity the resultant scattering attenuation images show an increase of attenuation toward the southwest from toya caldera which may correspond to deepening of the basement we also identify an area of low intrinsic and scattering attenuation at the summit of usu volcano which could be associated with old magma intrusions our results demonstrate a strong spatial relation between structural heterogeneities and attenuation processes in volcanic areas and confirm the efficiency of the method which can be used together with conventional imaging techniques

analysis of multiple scattering at vesuvius volcano italy using data of the tomoves active seismic experiment data from the tomoves active seismic experiment are used to study scattering effects in the shallow heterogeneous structure of vesuvius volcano seismograms from shots located on the volcano itself are characterised by spindle like envelopes small or missing p onsets missing s onsets and long codas seismograms from shots in the surroundings of the volcano on the contrary show clear and impulsive p and s onsets and short codas the different shapes of the envelopes can be explained by strong multiple scattering in the shallow heterogeneous eruptive material of the volcano and single scattering in the surrounding crust the seismograms of shots located on the volcano are modeled using the diffusion model with a diffusivity of d 0 1 km2 s for the frequency range of 2 16 hz assuming the dominance of s waves in the coda and a typical s wave velocity of around 1 5 km s this corresponds to a transport mean free path ltr of only 200 m which is 3 orders of magnitude smaller than for normal earth crust these results show that multiple scattering is an important effect which cannot be neglected in the modeling of seismic wave propagation in volcanic environments

properties of the near field term and its effect on polarisation analysis and source locations of long period lp and very long period vlp seismic events at volcanoes abstract seismicity that originates within volcanic magmatic and hydrothermal plumbing systems is characterised by wavelengths that are often comparable to or longer than the source receiver distance the effect of such a near field configuration must be explored when analysing these signals herein we summarise properties of near field observations for both a single force and moment tensor seismic sources we show radiation patterns of the near intermediate and far field terms for the source types that are most likely candidates for long lp and very long period vlp volcanic seismicity including a single force compensated linear vector dipole clvd a tensile crack and a pipe like source we find that the deviation of the first motion polarisation from the radial direction is significant in all planes except one whose normal is parallel to the symmetry axis if there is one of the source mechanism however this deviation is less pronounced or even negligible when there is a considerable volumetric component in the source as in the case of a tensile crack or pipe our location test shows that the accuracy of locations obtained using the semblance or cross correlation techniques is very significantly affected by the near field geometry this effect is especially pronounced for shallow sources such as often encountered on volcanoes and decreases with increasing source depth hence in practical applications on volcanoes 3d full waveform numerical simulation including topography and structural heterogeneities should be used in order to both validate location techniques and as an interpretational aid to reduce misinterpretations of location results

volcano topography structure and intrinsic attenuation their relative influences on a simulated 3d visco elastic wavefield the seismic wavefield recorded on volcanoes can be significantly influenced by path effects scattering from the topography and internal volcanic structure can play a dominant role in the recorded seismograms intrinsic attenuation is also thought to play an important role in the characteristics of volcano seismic signals we use 3d numerical modelling of wave propagation in elastic and visco elastic media including complex velocity models and topography to investigate the scattering and attenuation characteristics of synthetic seismograms we generate 5 distinct volcano models and simulate wave propagation through these models using shallow and deep double couple broadband sources we then analyse 129 synthetic seismograms calculated on the free surface the synthetic seismograms resemble vt a and vt b events the scattering effect of the topography alone is capable of producing complex seismograms the introduction of an internal velocity structure increases the duration of these seismograms while the introduction of intrinsic attenuation decreases the duration but not the complexity we fitted our synthetic seismograms to the diffusion in a half space model to quantify the scattering and attenuation coefficients the scattering quality factor measured on all 129 stations for all 5 volcano models was similar therefore we deduce that the topography appears to be the dominant scatterer the intrinsic attenuation quality factor for each of the specific models cannot be accurately recovered using the diffusion in a half space model the measured quality factor is not only sensitive to the attenuation properties but also to the structural properties in all cases the scattering is more dominant than the intrinsic attenuation

separation of scattering and intrinsic attenuation at asama volcano japan evidence of high volcanic structural contrasts abstract in this study we show 2d intrinsic and scattering q images of asama volcano obtained by analyzing 2320 waveforms from active data observed energy envelopes were fitted to the diffusion model and separate intrinsic and scattering q images were produced using a back projection method based on a gaussian type weighting function synthetic tests indicate robustness and reliability of the results areas of high scattering attenuation coincide with the volcanic edifice and the summit at which recent eruptions took place the intrinsic dissipation pattern shows a strong contrast between the east and west side of the volcanic structure with the low values observed in the west interpreted as solidified magma bodies our results demonstrate a strong relationship between structural heterogeneities and attenuation processes in volcanic areas and confirm the effectiveness of the present technique which can be used as an imaging tool complementary to conventional techniques

mechanisms of the nyos carbon dioxide disaster and of so called phreatic steam eruptions abstract during the night of august 21 1986 a huge volume of concentrated co 2 was emitted by the crater maar of nyos cameroon it killed more than 1700 people and all animal life as far as 14 km away two hypotheses have been put forward to account for this disaster the chronologically first one imputes it to have been a phreatic eruption exceptionally co 2 rich as had been the case in february 1979 on the dieng plateau in central java indonesia where the erupting crater was lake less the second one claims a limnic origin for the co 2 release through an overturn of the 220 m deep lake nyos the hypolimnium of which was supposed to be oversaturated by dissolved gas of volcanic origin the present paper points to six observed facts for which the eruptive hypothesis easily accounts and which the authors of the limnic one do ignore

a teleseismic delay time study across the central african shear zone in the adamawa region of cameroon west africa summary p wave relative teleseismic residuals were measured for a network of seismological stations along a 300 km profile across the adamawa plateau and the central african shear zone of central cameroon to determine the variation in crust and upper mantle velocity associated with these structures a plot of the mean relative residuals for the stations shows a long wavelength 300 km variation of amplitude 0 45 s the slowest arrivals are located over and just to the north of the faulted northern margin of the adamawa plateau the residuals do not correlate with topography surface geology or the previously determined crustal structure in any simple way the aki inversion technique has been used to invert the relative residuals into a 3 d model of velocity perturbations from a mean earth model the results show the region is divided roughly into three blocks by two subvertical boundaries striking ene and traversing both the crust and upper mantle down to depths greater than 190km the central block which is 2 per cent slower than the adjacent blocks roughly corresponds to the central african shear zone the adamawa plateau as an individual uplifted area is explained by the interaction of a regional anomalous upper mantle associated with the west african rift system and the central african shear zone which provided a conduit for heat flow to the surface

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

p wave velocity structure beneath asama volcano japan inferred from active source seismic experiment an active seismic survey with unprecedented density of seismometers found a high velocity zone to the west of the summit of asama volcano japan the high velocity zone coincides with an area of magma filled crack dike intrusion associated with the 2004 eruptions inferred from precise earthquake relocations and ground deformation modeling it also coincides with an area of high resistivity surrounded by low resistivity indicating that the solidification of magma due to repeating intrusions is responsible for the high velocity this thus endorses the magma pathway previously speculated by seismic and geodetic observations these findings demonstrate that dense seismic exploration combined with geophysical monitoring is an effective way to understand the dynamics of volcanic eruptions

a late holocene palaeoenvironmental record from lake tizong northern cameroon using diatom and carbon stable isotope analyses abstract a late holocene record based on diatom and stable carbon isotopes from lake tizong northern cameroon provides a history of environmental changes over the last 4100 years several coarser sediment layers among which the two younger ones are of pyroclastic origin interrupt the fine clayey sediment of the core the detailed chronology of the core supported by 24 radiocarbon 14c dates and proxies data results revealed an erosive phase registered in the sedimentary column from 2200 to 1500 cal bp the diatom ecological groups suggest that between 4100 and 2800 cal yrs bp the lake level was much higher than after corresponding to a relatively greater precipitation minus evaporation p e ratio as well as increased runoff in the lake catchment these conditions were favourable to the development of c3 plants in the lake catchment as indicated by lower 13c values and higher c n ratios than after this hydrological phase is also characterized by eutrophic turbid and probably circum neutral to alkaline waters after this episode higher 13c values between 2800 and 2500 cal bp suggest increased water use efficiency of terrestrial plants and or potentially more c4 plant debris input into the lake an indication of savannas patches developing due probably to changes in the rainfall distribution marked lake level declines are recorded at 2500 2200 2100 and at 1400 1000 cal yrs bp these low stands are characterized by higher inputs of windblown diatoms up to 4 2 than before which confirms that the ne trade winds were strengthening this corresponds primarily to a reduction in the p e ratio but probably also to greater inter annual or seasonal variability when drier periods or seasons became more prolonged and intense than previously consequently savannas were maintained as suggested by relatively higher than before 13c values as well as independently supported by regional pollen data after 1000 cal bp the lake level rose towards sub modern conditions with a deep neutral and eutrophic water column carbon stable isotopes suggest a reduction of organic matter input while savannas were maintained despite the return to more humid conditions the trends of climatic changes observed in the lake tizong reveal the variability in timing magnitude and regional extent of known climatic events

three dimensional kernel based coda attenuation imaging of caldera structures controlling the 1982 84 campi flegrei unrest abstract coda wave attenuation imaging has risen as a state of the art technique to depict volcanic structures using their dispersion effects the 1982 84 seismic and deformation unrest at campi flegrei caldera italy is a unique example of non eruptive volcanic activity in a structured caldera here we propose the first application of 3d coda attenuation kernels to image caldera structures at multiple frequencies during unrest using sensitivity kernels is necessary to assess the effective resolution of coda imaging in highly heterogeneous volcanoes the technique relies on the solution of paasschens equations in the framework of radiative transfer theory the results map coda attenuation in the 3d space without need of pre existent velocity models the resolution and stability of the inversion solutions were examined by changing the damping parameters and outputting the corresponding images inverting for different node spacings and performing checkerboard tests these tests show that the resolution of the multiple scattering model is much lower than that provided by a standard isotropic scattering and or single scattering technique the best resolution in our model is obtained between depths of 1 km and 3 km in the centre of the model between pozzuoli town and solfatara crater the results are discussed at a frequency of 3 hz due to both longer coda durations and broader kernel illumination in this frequency range coda based 3d imaging had so far failed to provide stable results the interpretation is performed based on the extensive geological and geophysical knowledge of the caldera high attenuation anomalies below solfatara and monte nuovo mark areas either saturated with water or enriched in molten rocks feeding the respective fumarole fields the flattening and horizontal elongation of these anomalies below 2 km depth is a manifestation of the blocking and spreading around of the rising hot magmatic fluids below a previously inferred high velocity low attenuation and highly deforming caprock this caprock is not uniform likely due to the remnants of erupted structure a sw to ne trending low attenuation and high velocity anomaly deeps down to 3 km under pozzuoli we infer that the high seismicity in the region is a consequence of the stress sustained by the caprock from a 4 km deep deformation source in 1983 84 on top of this source high coda attenuation corresponds to high vp vs ratios and high direct wave attenuation the region s characteristics are likely due to the accumulation of magmatic fluids above a magmatic sill

spatial distribution of scattering loss and intrinsic absorption of short period s waves in the lithosphere of japan on the basis of the multiple lapse time window analysis of hi net data summary propagation of short period s waves through the crust is strongly controlled by scattering loss and intrinsic absorption scattering loss controls the shape of the seismic envelope and the spatial distribution of the energy while intrinsic absorption produces an exponential decay as a function of time which is independent of the coordinates since both parameters have a different effect it is possible to compute them by means of the multiple lapse time window analysis mltwa in this paper high resolution maps of japan for both seismic s wave attenuation parameters are obtained by using the mltwa with data provided by the hi net seismic network the maps show strong regional variation of the parameters the variations depend mainly on the tectonic setting of each region and volcanism mechanisms in the scattering loss maps in the 1 2 hz map there is a very different behaviour between the northeast stronger scattering loss and the southwest much weaker scattering loss in the northeast of japan areas with strong scattering loss correspond mainly to the location of the volcanic arcs in southwest japan chugoku region and the west side of kii peninsula show strong scattering levels for the 4 8 hz and higher frequency bands in hokkaido strong scattering loss and intrinsic absorption can be observed for the lower frequency bands in the sendai plain we find strong scattering loss for all the frequency bands under all these areas low velocity anomalies have been detected in previous works in tohoku area the east side shows lower intrinsic attenuation than the west side this characteristic seems to extend to the southern part of hokkaido and to central japan in kanto area the values of intrinsic absorption are lower than in the surrounding areas but in the region around the itoigawa shizuoka tectonic line and in its western side strong absorption areas are observed the behaviour of each area for intrinsic absorption is similar to the behaviour observed in the q 1c maps the mltwa is based on the hypothesis of multiple isotropic scattering in a medium with the homogeneous distribution of scattering mean free path and intrinsic absorption although these hypotheses are very simple the results are very informative on the characteristics of each region and show the usefulness of studying the properties of scattered seismic waves in the understanding of the properties of the crust

particle transport over rough hillslope surfaces by dry ravel experiments and simulations with implications for nonlocal sediment flux 1 past studies of hillslope evolution have typically assumed that soil creep processes are governed by a linear relationship between local hillslope angle and transport distance the assumption of linear diffusion has fallen out of favor because when coupled with an expression of mass continuity it yields unrealistic hillslope profiles as a consequence a better understanding of the mechanics of sediment transport is needed here we report results from a series of flume experiments performed to investigate sediment transport by dry ravel a common soil creep process in arid and semiarid environments we find that at gentle slopes transport distances follow distributions characteristic of local transport as gradients steepen a fraction of the particles begins to exhibit nonlocal transport and that fraction increases rapidly with slope a stochastic discrete element model that couples an effective friction term with a shock term reproduces the results from the flume experiments suggesting that it can be used to explore the nature of particle transport on rough surfaces the model predicts that exponential distributions of transport distances on gentle slopes evolve into quasi uniform distributions on steep slopes and the transition occurs as slopes approach the angle of repose our results support previous findings that the angle of repose represents a threshold between friction and inertial regimes in addition we propose that the angle of repose represents a fuzzy boundary between local and nonlocal transport

sedimentary environmental changes and millennial climatic variability in a tropical shallow lake lake ossa cameroon during the holocene abstract the holocene environmental evolution of the shallow ossa lacustrine complex in cameroon is analysed on the basis of the present day sedimentary dynamics and principally by the study of five well dated cores sediment accumulation rates lithofacies and mineral content changes and various tracers of flux provenance are considered in connection with the pollen data at the shallower sites 1 2 m water depth during the dry season a moderate rise in lake level may have induced the transition from hydromorphic marshy conditions gleys to lacustrine conditions muds ca 8000 cal bp at the easternmost site a moderate fall may have generated the opposite process ca 7000 cal bp in the near northern part a marked decrease in sediment accumulation rate between 5000 and 3000 cal bp is apparent in some cores coinciding with an increasing discontinuity of the particulate supply during this interval the weakening of monsoon rainfall is associated to an increasingly seasonal regime characterized by lower and sporadic fluxes this decrease corresponds to a northern shift of equatorial climatic conditions with the main dry season occurring during the boreal summer during the time interval between ca 2800 and 2000 cal bp the return of tropical climatic conditions induced the opening of the vegetation associated with more intensive erosion increasing cyperaceae may indicate flooding of areas suitable for colonisation until 2800 cal bp the first overflow of the sanaga river into lake ossa occurred after ca 5800 cal bp with a ne sw depositional axis of coarse material transport of suspended matter in the surface waters northward was probably induced by prevailing sw winds the timing of this climatic evolution is independently supported by other lake sediment records from the forest domain of west africa and can be compared with other cyclical phenomena such as bond and dansgaard oeschger as well as solar oscillations

sedimentation and palaeoenvironment in crater lake barombi mbo cameroon during the last 25 000 years lake barombi mbo is situated in a maar crater of the cameroon volcanic chain sediment cores were recovered with a livingstone corer this paper presents data on core bm6 23 5 m long from a water depth of 110 m the sediments are mainly organic matter rich clays 5 to 10 total organic carbon showing alternating brown and yellowish horizontal laminae on a cm scale the lower part of a couplet basal sublamina is rich in siliciclastic quartz mica grains sponge spicules and documents the deposition of flood detritus the upper unit upper sublamina is composed of grey to bluish clay which becomes green toward the top with frequently yellow layered concretions of siderite it corresponds to quiet conditions with settling of fine clayey particles from suspension the overall recurrence rate of these laminae is about 15 years this frequency is similar to present day large flood events in this intertropical zone from 14 000 to 20 000 yrs bp the sediment accumulation rate was quite low 15 30 g cm 2 10 3 yrs with less abundant precipitation pedogenic clay formed from mica family minerals from 12 000 yrs bp throughout the holocene the rate of accumulation increased 40 g cm 2 10 3 yrs and increasing precipitation favoured the pedogenic formation of kaolinites turbidity currents became less important to the overall sedimentation plankton production remained low documented by organic matter which is more of the exinite than the alginite type siderite concretions occur as early diagenetic products possibly related to alkalinity in anoxic waters at the sediment water interface which limited the formation of fe3 thin ash layers occur between 11 5 and 18 m depth in core bm6 bearing witness to several volcanic events during the late quaternary sediments are disturbed below 21 m with folded laminations and inverse ages these probably result from a slump glide of lower slope sediment but could also signal a possible gas event

a back projection method for imaging large scale lateral variations of lg coda q with application to continental africa summary a new method is developed which uses back projection tomography to regionalize large scale lateral variations of coda q for lg waves which have traversed long continental paths successful use of this method requires precise and stable single trace measurements of lg coda q xie nuttli 1988 the method converges rapidly and requires minimal computer storage it also allows quantitative estimation of resolution and error in imaging lateral variations of coda q the spatial resolution of this method is limited by the uneven spatial coverage of the data base by our limited knowledge of lg coda generation and by the trade off between the stability and the spatial resolution of the coda q inversion the method is applied to a large set of digital lg coda data from africa where large scale lateral variations of lg coda q are found to correlate well with major tectonic features most of africa is stable and like other stable regions has relatively high coda q values the lowest values of coda q are associated with the african rift system other regions of low q values include the atlas mountains and cape fold belt regions of mesozoic and younger deformation the lateral variation of frequency dependence of lg coda q correlates in most regions with that of q at 1 hz our analysis of the spatial resolution of this method indicates that the resolving power of lg coda q imaging is comparable to that of velocity tomography using long period surface waves using empirical approaches we estimate that uncertainties in lg coda q and its power law frequency dependence parameter are less than about 60 and about 0 2 respectively for most of africa

scattering behaviour at merapi volcano java revealed from an active seismic experiment summary the seismic structure of the stratovolcano merapi java indonesia was studied using an active seismic experiment three 3 km long seismic profiles each consisting of up to 30 three component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level the detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting the seismic experiment at merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome where the sources of most of the natural volcanic seismic events are located the cone of merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material additionally the topography of the erosion valleys leads to an irregular deposition which cannot be described by a simple 1 d layering these inhomogeneities have a strong influence on seismic signals the direct p and s waves are attenuated quickly and show only small amplitudes on seismograms the energy lost from the direct waves however is not changed into heat but scattered and can be observed as seismic coda following the direct waves the observed seismograms show a spindle like amplitude increase after the direct p phase this shape of the envelope can be explained by the diffusion model according to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves besides the envelope the coherence and polarization properties of the wavefield also indicate strong scattering only the first onset shows coherence over a station spacing of 100 m whereas the late phases carrying the major part of the energy are mainly incoherent the horizontal components of the seismograms have larger amplitudes than the vertical component but within the horizontal plane the polarization is almost arbitrary corresponding to waves arriving from scatterers located arbitrarily in space as a result of the inversion using the diffusion model we obtain values of the s wave scattering attenuation coefficient gs and the s wave intrinsic absorption coefficient gi in the frequency range of 4 20 hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption gs gi the mean free path of s waves is as low as 100 m gs1 100 m the scattering coefficient is independent of frequency gsyf 0 0 whereas the coefficient of intrinsic attenuation increases with increasing frequency giyf 1 6 the natural seismic signals at merapi volcano show similar characteristics to the artificial shots the first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves therefore these signals appear to be strongly affected by multiple scattering also

the holocene sedimentary and pyroclastic accumulations of two crater lakes mbalang tizong of the volcanic plateau of adamawa cameroon palaeoenvironmental reconstruction this paper presents the results from field observations geochemical and mineralogical analyses radiocarbon dating and magnetic susceptibility of the holocene sediments of two crater lakes mbalang and tizong located within the woody savanna of the adamawa plateau cameroon in the mbalang core m4 with an age of 7318 cal bp at the base the first 2000 years record indicates a relatively wet climate deduced from the recurrence of quartz rich sandy microbeds the next millennia are marked by a monotonous sedimentation interpreted as a relatively dry phase the accumulation rate falls from 1 00 1 40 to 0 70 mm yr in the last 100 years the base of the tizong core t2 is dated to 4105 cal bp the sedimentation is frequently interrupted by interstratifications of pyroclastic beds from c 3263 to 1391 cal bp well evidenced by their high magnetic susceptibility values the high accumulation rate 1 58 mm yr integrates both allochthonous volcanic ashes and autochthonous intense proliferation of chlorophyceaea the ngaoundere region in the southern forest region reveals a humid phase between c 7943 and 5603 cal bp the later long lasting dry tendency makes it difficult to particularly distinguish the c 3210 1945 cal bp dry periods recorded in the forest region of cameroon nevertheless signs from mbalang pollens and tizong waters bear witness to an important drying tendency during this period in lake chad after the successive highest lake levels recorded between c 8500 and 6300 cal bp the level of this lake was declining for the last three millennia

coda q distribution in the iberian peninsula summary several attenuation studies have established a frequency dependence law of the anelastic attenuation factor q in the form q qo f fo v for the approximate 1 10 hz frequency range we propose a method that leads to the determination of q which is a function of the reference frequency fo and the real exponent v with a single station to carry out the problem we determine a set of master curves as a function of y we discuss the method and the different features of the master curves when it is applied to the complicated regions of the iberian peninsula and to several instruments with different responses using this new method and the seismographic stations available in the iberian peninsula we have mapped iso qo lines at a reference frequency of 1 hz applying inversion methods the q values determined for iberia vary between about 100 and about 600 values close to 100 correspond to the southern part of iberia in general q values increase from south to north with values about 600 near the nw part of iberia the pyrenees mountains and adjacent areas present q values between about 200 and about 350 these results suggest a strong qo lateral variation in iberia a considerable frequency dependence of coda q has also been determined the v values vary between 0 3 and 0 8 the q values obtained in the iberian peninsula show very good agreement with several q values obtained in other regions of the world comparison between the iso q lines and other geophysical parameters like regional variations of p velocities heat flow isoseismal intensity distribution and crustal thickness indicates that lower q values are associated with higher isoseismal intensity attenuation higher heat flow lower p velocities and thinner crust

late holocene paleoclimatic changes in western central africa inferred from mineral abundance in dated sediments from lake ossa southwest cameroon abstract minerals derived from catchment soils were determined using ftir spectroscopy in the well dated core ow4 from lake ossa a lowland rainforest area in cameroon this quantification provides a hydrologic record indicating that the magnitude of runoff events and by inference rainfall pattern has varied during the late holocene the comparison between minerogenic inputs and vegetation changes improves the understanding of the inferred climate dynamics since at least 5400 cal yr b p the paleomonsoon rainfall intensity decreased as shown by a general decrease in mineral fluxes this observation is consistent with a gradual weakening of the boreal summer insolation in tropical latitudes however the major vegetational change lags behind the onset of the decrease in mineral fluxes from 2800 to ca 1000 cal yr b p the forest receded the amount of rainforest taxa decreased and is replaced by pioneer trees and poaceae when the mineral fluxes attained their lowest values this episode of maximum dryness is attributed to an abrupt climatic event of global significance which is superimposed onto the paleomonsoon variability it is related to a cold event which in turn produced a change in the lower atmospheric circulation that was characterized by a strengthening of northern trade winds probably correlated with sea surface temperature variations in the eastern tropical atlantic area

a model for fire induced sediment yield by dry ravel in steep landscapes sediment flux from hillslopes to channels commonly increases following wildfires with implications for the carbon cycle river habitats and debris flow hazards although much of this material is transported via dry ravel existing ravel models are not applicable to hillslopes with gradients greater than the angle of repose which can constitute the majority of mountainous terrain to fill this knowledge gap we develop a continuity model for sediment storage by vegetation dams on steep hillslopes to predict sediment yields following wildfire the maximum volume of sediment stored prior to wildfire is set to be a function of vegetation density the capacity of plants to impound sediment and the contributing hillslope area time is required after fire to establish vegetation and replenish hillslope sediment storage which introduces vegetation regrowth rate soil production rate and fire recurrence interval as important variables that affect ravel yield model results for the san gabriel mountains california predict that sediment yield can increase by several orders of magnitude following fire these results are consistent with field data of ravel yield 30 mm per contributing area of hillslope in 5 months we collected following the 2009 station fire as well as postfire sediment flux recorded by 93 debris basins in contrast to previous work our model shows that heightened postfire sediment yields can be explained by a change in hillslope sediment storage independent of major changes in the soil production rate and landscape form over geomorphic timescales

vegetation and wildfire controls on sediment yield in bedrock landscapes steep rocky landscapes commonly exhibit high sediment yields and are especially sensitive to climate tectonics and wildfire predicting landscape response to these perturbations demands a quantitative understanding of erosion processes however existing models for hillslope sediment production and transport do not apply to landscapes with patchy soil and slopes that exceed the angle for sediment stability here we present field measurements in southern california usa which indicate that sediment storage on steep slopes is enabled by vegetation that traps sediment upslope we find that the storage capacity of unburned vegetation dams follows a geometric scaling model with a cubic dependence on effective plant width and an inverse dependence on local slope measured sediment volumes behind burned vegetation dams indicate a loss of at least 75 relative to unburned dams and when expanded to the catchment scale our measurements match records of postfire sediment yield from nearby retention basins contrary to existing models our observations indicate that wildfire induced sediment yield is driven by transient storage and release of sediment by vegetation dams rather than increased bedrock to soil conversion rates without a feedback between soil production and wildfire fire may play little role in long term landscape evolution and increasing fire frequency in response to climate change may not result in heightened sedimentation hazards due to supply limitations

monte carlo simulation of seismogram envelopes in scattering media the analysis of the seismogram coda envelopes of local and regional earthquakes is one of the most effective strategies for investigating the heterogeneous lithospheric structure characterized by the seismic scattering and attenuation in order to synthesize the coda envelope we introduce a numerical scheme called the direct simulation monte carlo method which has been used in the field of the kinetic theory of gases because of the simplicity of the algorithm the method has several advantages over previous methods in terms of the flexibility of the numerical calculation to incorporate various factors required to construct realistic seismogram envelopes on the basis of coda envelope simulations including multiple scattering we show that an increase of seismic velocity with depth severely affects the shape of the coda envelope the effects of ray bending due to the velocity increase at the moho and the reflection at the free surface are clearly found in the synthesized envelope for a shallow earthquake our simulation demonstrates that the amplitude of the envelope is magnified by stagnation of seismic energy at shallow depths due to the positive velocity gradient with depth because of this effect for an a priori assumption of a homogeneous velocity model the measurement of the scattering coefficient by conventional methods may be overestimated

spatial variations of seismic attenuation and heterogeneity in the pyrenees coda q and peak delay time analysis abstract lateral variations of seismic attenuation in the pyrenees are explored from the analysis of local earthquake records scattering loss and intrinsic absorption both control the propagation of short period s waves through the crust the role of intrinsic and scattering attenuation is analyzed in two steps firstly the coda quality factor q c which quantifies the energy decay of coda waves is estimated at large lapse time in five frequency bands and interpreted as intrinsic absorption next we systematically measure the peak delay time defined as the time lag from the direct s wave onset to the maximum amplitude arrival this parameter quantifies the strength of multiple forward scattering due to random inhomogeneities along the seismic ray path comparison of coda q and peak delay time measurements allows a qualitative interpretation of the origin of seismic attenuation scattering absorption in the pyrenean crust at low frequency coda q variations mainly depend on the tectonic units of the pyrenees with stronger absorption in sedimentary basins and smaller absorption in paleozoic basements at high frequency coda q is low at the location of neogene structures in the eastern pyrenees a more enigmatic low q c anomaly is also observed at the location of the maladeta massif in the central pyrenees in all frequency bands peak delay time measurements systematically show stronger scattering in the western pyrenees in the labourd mauleon area absorption and scattering are both important at low frequency the western pyrenees also correspond to a high velocity density anomaly revealed from tomography and gravity data analysis this suggests that the high level of inhomogeneities and absorption may be related to intrusion of mantle and or lower crustal materials in the eastern pyrenees absorption appears dominant over scattering at high frequency we hypothesize that the strong absorption observed in this area may be related to volcanic structures

absorption and scattering 2 d volcano images from numerically calculated space weighting functions acknowledgments yosuke aoki and an anonymous reviewer greatly improved the quality of the paper all calculations were made with mathematica 10tm discussions with marie calvet danilo galluzzo mario la rocca salvatore de lorenzo jessie mayor and ludovic margerin are gratefully acknowledged the authors are supported by medsuv european project and by spanish project ephestos cgl2011 29499 c02 01 and nowaves tec2015 68752 the tides eu travel cost action provided travel money to support cooperation between luca de siena and the other authors

late holocene climatic changes in west africa a high resolution diatom record from equatorial cameroon abstract holocene climatic changes in west africa are usually explained by increased decreased activity of the monsoon from the guinean gulf toward the continent according to a diatom record from lake ossa 3 50 n 9 36 e we suggest that in the near coastal areas of cameroon phases of intensification of the monsoon were marked by reduced precipitation and reduced evaporation conditions nowadays prevailing south of the equator 4 5 s during the austral winter lake ossa is a shallow lake located in one of the rainiest area of the african rain forest belt during the wet season march november it is fed by acid meteoric waters entailing low ph in the lacustrine waters during the dry season december february groundwater discharges allow the persistence of acid waters near the borders of the lake but in the inner parts the waters tend to be alkaline alkaliphilous diatoms are abundant in the surface sediment samples and are used as indicators of low precipitation at that time atmospheric dust containing reworked diatoms from saharan quaternary deposits is transported by the northern trade winds and reaches the ossa area wind blown diatoms are considered as a signature of the northern trade winds a diatom record from the western deep part of lake ossa has provided climatic data for the mid late holocene at a resolution of 50 60 years a major climatic change at 2700 cal yr bp was marked by the appearance of wind blown diatoms a millennial scale alternation between low and high precipitation episodes is recorded during the last 5500 years the low precipitation episodes before 2700 cal yr bp are interpreted as a consequence of a northward extension of the climatic conditions that nowadays characterize the southern congo during the austral winter when the monsoon extends into west africa and reaches the northern sub tropical latitudes the effects of low precipitation on the water balance and on the rain forest were obliterated by an extremely low evaporation between 2700 and 1300 cal yr bp precipitation was high and the rain forest intensively disturbed in response to convective storms a low precipitation episode between 1300 and 600 cal yr bp is explained contrarily to the previous similar episodes by tropical rainfalls located farther south than today during a larger part of the year the modern climate settles at about 600 cal yr bp the climatic oscillations on a millennial time scale were apparently coincident with temperature changes in the northern and southern atlantic suggesting that the monsoon over west africa was essentially driven by interactions between both hemispheres this interpretation is in agreement with available data from other equatorial and sub tropical regions of west africa

denudation processes and rates in the transverse ranges southern california erosional response of a transitional landscape to external and anthropogenic forcing 1 quantification of denudation in the transverse ranges of california permits reconstruction of spatial and temporal variations in erosion that represent both the response and evolution of interacting hillslopes and channels on the southern front of the san gabriel mountains observational records of the infilling of debris basins and dams define twentieth century landscape erosion rates averaging 1 6 and 0 9 mm yr 1 respectively although all major sediment transport occurs during intense winter storms debris production on hillslopes is greatly enhanced by recurrent fires consequently in this populated region anthropogenic fires have augmented the natural erosion rates we perform a global inversion to estimate the role of precipitation intensity burned areas and local slope on catchment denudation rates after subtracting the effects of anthropogenic fires we estimate landscape denudation rates given natural fire ignition rates increased fire during the past century has augmented sediment production in debris basins by an average of 60 and individual basins show increases up to 400 to identify the dominant hillslope erosion processes the volumetric contribution of landslides was estimated using repeat aerial photographs for the same time interval over which the debris basins have been operative between 1928 and 1973 landsliding produced only 10 of the sediment in debris basins even in the long term when infrequent but volumetrically important landslides occur bedrock landslides appear to contribute a maximum of 50 to the long term landscape denudation previous mapping of soil slippage in the san dimas experimental forest within the san gabriel mountains rice et al 1969 rice and foggin 1971 indicates that shallow landsliding is likely to be the dominant modern hillslope erosion process when compared to incision rates derived from a fluvial shear stress model and to exhumation rates based on low temperature thermochronological data blythe et al 2000 modern natural erosion rates are comparable to denudation rates since the pliocene comparisons of modern erosion rates suggest that debris production on hillslopes and first order channels is directly dependent on vegetation cover and precipitation intensity for higher order channels drainage areas 2 km2 only major storms convey the sediments down valley during the past century some temporal decorrelation occurs between small scale and large scale catchments because hillslope produced sediment is stored in second order and higher channels until major storms mobilize it thus the larger fluvial network damps the episodic fire induced hillslope sediment pulses that occur within small watersheds at a longer temporal scale however uplift and denudation may have been sustained sufficiently long in much of the san gabriel mountains for the topography to reach a macroscale steady state in contrast to rapidly eroding 2 mm yr 1 ranges for which quantification of bedrock landsliding will approximate the sediment flux the san gabriel mountains occupy a niche of intermediate rates 0 1 1 0 mm yr 1 in which a broad suite of hillslope processes including shallow seated and deep seated landslides debris flows and wet and dry ravel contribute to the sediment flux

influence of near surface volcanic structure on long period seismic signals and on moment tensor inversions simulated examples from mount etna 1 long period lp seismicity on volcanoes is thought to be associated with moving fluids or resonating fluid filled conduits hence lp moment tensor mt source inversions might have a direct bearing on our understanding of the plumbing system using 3 d full wavefield simulations and 2 d sensitivity kernels in a digital elevation model of mount etna we investigate the influence of near surface volcanic structure on lp signals and on moment tensor inversions contrary to common wisdom in crustal seismology we find that despite their relatively long wavelengths lps are severely distorted by near surface structures including layering and topographic features in particular near surface low velocity structures which are commonly observed on volcanoes play a critical role in controlling the nature of lp signals if not accounted for these path effects leak into the source solution leading to the emergence of erroneous source geometries spurious forces and incorrect source time functions this is particularly problematic if one adopts an unconstrained solution space for the source with many free parameters hence there is a fine balance in the trade off between the velocity model and the source in the absence of high resolution near surface velocity control we demonstrate the importance of employing a priori source information from other fields e g structural geology for shallow lps constraining the number of free parameters in the inversion a probabilistic approach should then be taken as the model with the best fit is not necessarily the true solution

two dimensional seismic attenuation images of stromboli island using active data in this work we present intrinsic and scattering seismic attenuation 2 d images of stromboli volcano we used 21 953 waveforms from air gun shots fired by an oceanographic vessel and recorded at 33 inland and 10 ocean bottom seismometer seismic stations coda wave envelopes of the filtered seismic traces were fitted to the energy transport equation in the diffusion approximation obtaining a couple of separate qi and qs in six frequency bands using numerically estimated sensitivity kernels for coda waves separate images of each quality factor were produced results appear stable and robust they show that scattering attenuation prevails over intrinsic attenuation the scattering pattern shows a strong concordance with the tectonic lineaments in the area while an area of high total attenuation coincides with the zone where most of the volcanic activity occurs our results provide evidence that the most important attenuation effects in volcanic areas are associated with the presence of geological heterogeneities

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

hillslope response to tectonic forcing in threshold landscapes hillslopes are thought to poorly record tectonic signals in threshold landscapes numerous previous studies of steep landscapes suggest that large changes in long term erosion rate lead to little change in mean hillslope angle measured at coarse resolution new lidar derived topography data enables a finer examination of threshold hillslopes here we quantify hillslope response to tectonic forcing in a threshold landscape to do so we use an extensive cosmogenic beryllium 10 10 be based dataset of catchment averaged erosion rates combined with a 500 km 2 lidar derived 1 m digital elevation model to exploit a gradient of tectonic forcing and topographic relief in the san gabriel mountains california we also calibrate a new method of quantifying rock exposure from lidar derived slope measurements using high resolution panoramic photographs two distinct trends in hillslope behavior emerge below catchment mean slopes of 30 modal slopes increase with mean slopes slope distribution skewness decreases with increasing mean slope and bedrock exposure is limited above mean slopes of 30 our rock exposure index increases strongly with mean slope and the prevalence of angle of repose debris wedges keeps modal slopes near 37 resulting in a positive relationship between slope distribution skewness and mean slope we find that both mean slopes and rock exposure increase with erosion rate up to 1 mm a in contrast to previous work based on coarser topographic data we also find that as erosion rates increase the extent of the fluvial network decreases while colluvial channels extend downstream keeping the total drainage density similar across the range our results reveal important textural details lost in 10 or 30 m resolution digital elevation models of steep landscapes and highlight the need for process based studies of threshold hillslopes and colluvial channels

attenuation and scattering tomography of the deep plumbing system of mount st helens we present a combined 3 d p wave attenuation 2 d s coda attenuation and 3 d s coda scattering tomography model of fluid pathways feeding systems and sediments below mount st helens msh volcano between depths of 0 and 18 km high scattering and high attenuation shallow anomalies are indicative of magma and fluid rich zones within and below the volcanic edifice down to 6 km depth where a high scattering body outlines the top of deeper aseismic velocity anomalies both the volcanic edifice and these structures induce a combination of strong scattering and attenuation on any seismic wavefield particularly those recorded on the northern and eastern flanks of the volcanic cone north of the cone between depths of 0 and 10 km a low velocity high scattering and high attenuation north south trending trough is attributed to thick piles of tertiary marine sediments within the st helens seismic zone a laterally extended 3 d scattering contrast at depths of 10 to 14 km is related to the boundary between upper and lower crust and caused in our interpretation by the large scale interaction of the siletz terrane with the cascade arc crust this contrast presents a low scattering 4 6 km2 hole under the northeastern flank of the volcano we infer that this section represents the main path of magma ascent from depths greater than 6 km at msh with a small north east shift in the lower plumbing system of the volcano we conclude that combinations of different nonstandard tomographic methods leading toward full waveform tomography represent the future of seismic volcano imaging

shallow resistivity structure of asama volcano and its implications for magma ascent process in the 2004 eruption asama volcano is an active volcano with many historical records of vulcanian eruptions its most recent eruptions occurred in 2004 at the summit crater in this paper we argue the resistivity structure shallower than 3 km obtained by a dense magnetotelluric survey the magnetotelluric data were obtained at 74 measurement sites mainly along the four survey lines across the volcano the resistivity profiles obtained by two dimensional inversions are characterized by a resistive surface layer and an underlying conductive layer the dominant feature of the profiles is the existence of resistive bodies at a depth range of a few hundred meters to a few kilometers surrounded by a highly conductive region considering that the location of resistive bodies correspond to the old eruption centers one corresponds to the 24 ka collapse caldera and the other to the 21 ka lava dome the resistive bodies imply zones of old and solidified intrusive magma with low porosity because geothermal activities exist near the resistive bodies the enclosing highly conductive regions are interpreted as a hydrothermal system driven by the heat from the old solidified magma beneath the resistive body under the collapsed caldera intrusion of magma is inferred from the studies of volcano tectonic earthquakes and continuous global positioning system gps observation implying the structural control of magma activity within the volcano in this study we propose that the magma ascent was impeded by the old and solidified remnant magma and partly migrated horizontally to the east and finally ascended to the summit resulting in the 2004 eruptions