global upper mantle structure from finite frequency surface wave tomography 1 we report global shear wave velocity structure and radial anisotropy in the upper mantle obtained using finite frequency surface wave tomography based upon complete three dimensional born sensitivity kernels because wavefront healing effects are properly taken into account finite frequency surface wave tomography improves the resolution of small scale mantle heterogeneities especially for deep anomalies that are constrained by the longest period surface waves in our finite frequency model ffsw1 the globally averaged radial anisotropy shows a transition from positive sh sv to negative anisotropy sv sh at about 220 km consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths the radial anisotropy beneath cratons and the old pacific plate agrees well with previous studies however our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid ocean ridges a feature that is not present in previous upper mantle models more interestingly the depth extent of the ridge anomalies is distinctly different beneath fast and slow spreading centers anomalies beneath fast spreading centers are stronger but the strength decreases rapidly below 250 km in contrast beneath slow spreading centers such as the northern mid atlantic ridge and the red sea anomalies extend down at least to the top of the transition zone the different depth extent of the ridge anomalies suggests that the primary driving force of slow spreading seafloor may be different from that of fast spreading seafloor and that active upwelling beneath slow spreading ridges may play a major role in the opening of the seafloor

lithospheric structure of the central andes based on surface wave dispersion 1 shear wave velocity is very sensitive to temperature anomalies and partial melt and can provide important insights on the state of the lithosphere with that aim in mind phase velocities of rayleigh and love waves have been inverted for the regionalized shear wave velocity structure of the lithosphere across the central andes this inversion reveals strong lateral variations of vs both across the range and along strike in the altiplano crust in the upper crust the main features of our models are prominent low velocity anomalies probably related to partial melt below the los frailes ignimbrite complex and the southern altiplano at lower crustal level the altiplano is characterized by lower vs than the surrounding regions we find that the transition from the altiplano to the puna is associated with a 7 km thickening of the crust at mantle depths the nazca plate is found to be overlaid by a dipping low velocity zone with decreasing intensity with depth our results favor the idea of a cold mantle lid underlying the whole central andes

solute budgets and denudation rate estimates for a mid wales catchment input output budgets for thirteen solutes for a small moorland catchment in upland mid wales show a net loss of all chemical elements from the catchment except hydrogen ion and inorganic nitrogen these two are being assimilated by the catchment the solute budgets are affected by geochemical processes occurring within the catchment a solutional denudation rate estimate of 2 9 b is derived from the silicon budget and a denudation rate of 3 5 b from the loss of suspended sediment and bedload from the catchment

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

wave theoretical inversion of teleseismic surface waves in a regional network phase velocity maps and a three dimensional upper mantle shear wave velocity model for southern germany summary using teleseimic surface wave data from 110 selected earthquakes recorded at 10broad band stations in southern germany we construct phase velocity maps of rayleigh waves for southern germany in a further step these maps are inverted for a three dimensional model of the sv velocity of the upper 200 km of the mantle we attempt to take into account the effect of heterogeneous structure outside the study region by jointly inverting the data for heterogeneous phase velocity inside the study region and the distortion of the incoming wavefields by the surrounding structure the total wavefield in the study region is computed with a scattering formalism which includes multiple forward scattering and single backscattering since in principle the data can be perfectly fit by the incoming wavefields without any heterogeneous structure inside the study area we impose additional constraints on the incoming wavefields to reduce the non uniqueness the most important constraint is an energy criterion which states that the energy of the modelled wavefield in the study area averaged over many events should be equal to the energy sampled by the stations we demonstrate that enforcing this criterion generates phase velocity maps with heterogeneous structure nevertheless we are able to satisfy the energy criterion without any heterogeneous structure at the price of an only slightly increased data misfit hence it must be concluded that a seismic network of size and station density such as the one used in this study is still insufficient to demonstrate convincingly the existence of heterogeneities in the network area using teleseismic surface waves any reasonable structure combined with the appropriate incoming wavefields would allow an acceptable fit of our data this frustrating conclusion of course applies to all other comparable studies which use teleseismic surface waves although we cannot convincingly show that any phase velocity map we find should be preferred over others we are able to obtain good reconstructions of test structures from realistic synthetic data with the same station and event distribution as the real data moreover we find that the geometric pattern of the phase velocity maps obtained from real data depends only weakly on the constraints applied in the inversion while the amplitude of the phase velocity perturbations is almost completely determined by the constraints for all periods considered the fit to the data is extremely good the reduction of the quadratic misfit relative to the case of plane incoming waves and no structure is dramatic for the shorter periods the 3 d model of vertical shear wave velocity down to a depth of 200 km exhibits a basic division into four quadrants separated by a vertical plane intersecting the surface along a nearly west east line and a horizontal plane at about 130 km depth the northern rants show high velocities in the top 120 km and low velocities below 140 km the opposite is the case for the southern quadrants an exception to this general feature is a pronounced low velocity zone in the northwestern corner of the region

variability in eruption style and associated very long period events at fuego volcano guatemala 1 repeated short term deployments of seismic infrasound video and gas emission instruments at fuego volcano guatemala have revealed three types of very long period vlp events associated with conduit sealing pressure accumulation and release in 2008 ash rich explosions issued from a vent on the western flank and produced one type of vlp type 1 impulsive bomb rich explosions from the summit vent in 2009 produced a shorter period vlp type 2 but also generated ash release type 3 vlp events occurred during ash free exhalations from the summit in 2008 and had waveform shapes similar to type 2 events weak infrasound records for type 1 explosions compared to type 2 suggest lower pressures and higher magma porosity for type 1 type 3 events correlate with spikes in so2 emission rate and are driven by partial sealing and rapid release of ash free gas at the summit vent variations in the vlp period may provide a new tool for monitoring conditions within the conduit

tilt prior to explosions and the effect of topography on ultra long period seismic records at fuego volcano guatemala 1 ground tilt is measured from broadband seismic records prior to frequent explosions at fuego volcano guatemala we are able to resolve tilt beginning 20 30 minutes prior to explosions followed by a rapid reversal in deformation coincident with explosion onsets the tilt amplitude and polarity recorded on the horizontal channels vary from station to station such that the steep and unusual topography of the upper cone of fuego appears to affect the ultra long period signals we account for the effect of topography and attempt to constrain the tilt source depth and geometry through finite difference modeling the results indicate a shallow spherical pressure source and that topography must be considered when attempting to model tilt sources at volcanoes with steep topography the tilt signals are interpreted as pressurization of the shallow conduit beneath a crystallized plug followed by elastic deflation concurrent with explosive pressure release

eruption dynamics at mount st helens imaged from broadband seismic waveforms interaction of the shallow magmatic and hydrothermal systems 1 the current eruption at mount st helens is characterized by dome building and shallow repetitive long period lp earthquakes waveform cross correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks stacked spectra of these events display multiple peaks between 0 5 and 2 hz that are common to most stations lower amplitude very long period vlp events commonly accompany the lp events we model the source mechanisms of lp and vlp events in the 0 5 4 s and 8 40 s bands respectively using data recorded in july 2005 with a 19 station temporary broadband network the source mechanism of the lp events includes 1 a volumetric component modeled as resonance of a gently nnw dipping steam filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2 a vertical single force attributed to movement of the overlying dome the vlp source which also includes volumetric and single force components is 250 m deeper and nnw of the lp source at the sw edge of the 1980s lava dome the volumetric component points to the compression and expansion of a shallow magma filled sill which is subparallel to the hydrothermal crack imaged at the lp source coupled with a smaller component of expansion and compression of a dike the single force components are due to mass advection in the magma conduit the location geometry and timing of the sources suggest the vlp and lp events are caused by perturbations of a common crack system

rayleigh wave phase velocities small scale convection and azimuthal anisotropy beneath southern california 1 we use rayleigh waves to invert for shear velocities in the upper mantle beneath southern california a one dimensional shear velocity model reveals a pronounced low velocity zone lvz from 90 to 210 km the pattern of velocity anomalies indicates that there is active small scale convection in the asthenosphere and that the dominant form of convection is three dimensional 3 d lithospheric drips and asthenospheric upwellings rather than 2 d sheets or slabs several of the features that we observe have been previously detected by body wave tomography these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern sierra nevada and walker lane region sinking lithosphere beneath the southern central valley upwelling beneath the salton trough and downwelling beneath the transverse ranges our new observations provide better constraints on the lateral and vertical extent of these anomalies in addition we detect two previously undetected features a high velocity anomaly beneath the northern peninsular range and a low velocity anomaly beneath the northeastern mojave block we also estimate the azimuthal anisotropy from rayleigh wave data the strength is 1 7 at periods shorter than 100 s and decreases to below 1 at longer periods the fast direction is nearly e w the anisotropic layer is more than 300 km thick the e w fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms pure shear in the lithosphere due to n s tectonic shortening and simple shear in sublithosphere mantle due to mantle flow

arrival angles of teleseismic fundamental mode rayleigh waves across the alparray the dense alparray network allows studying seismic wave propagation with high spatial resolution here we introduce an array approach to measure arrival angles of teleseismic rayleigh waves the approach combines the advantages of phase correlation as in the two station method with array beamforming to obtain the phase velocity vector 20 earthquakes from the first two years of the alparray project are selected and spatial patterns of arrival angle deviations across the alparray are shown in maps depending on period and earthquake location the cause of these intriguing spatial patterns is discussed a simple wave propagation modelling example using an isolated anomaly and a gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths this indicates that arrival angle information constitutes useful additional information on the earth structure beyond what is currently used in inversions

very long period conduit oscillations induced by rockfalls at kilauea volcano hawaii 1 eruptive activity at the summit of kilauea volcano hawaii beginning in 2010 and continuing to the present time is characterized by transient outgassing bursts accompanied by very long period vlp seismic signals triggered by rockfalls from the vent walls impacting a lava lake in a pit within the halemaumau pit crater we use raw data recorded with an 11 station broadband network to model the source mechanism of signals accompanying two large rockfalls on 29 august 2012 and two smaller average rockfalls obtained by stacking over all events with similar waveforms to improve the signal to noise ratio to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account we apply a new waveform inversion method that accounts for the contributions from both translation and tilt in horizontal seismograms through the use of green s functions representing the seismometer response to translation and tilt ground motions this method enables a robust description of the source mechanism over the period range 1 1000 s the vlp signals associated with the rockfalls originate in a source region 1 km below the eastern perimeter of the halemaumau pit crater the observed waveforms are well explained by a simple volumetric source with geometry composed of two intersecting cracks including an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east each rockfall is marked by a similar step like inflation trailed by decaying oscillations of the volumetric source attributed to the efficient coupling at the source centroid location of the pressure and momentum changes induced by the rock mass impacting the top of the lava column assuming a simple lumped parameter representation of the shallow magmatic system the observed pressure and volume variations can be modeled with the following attributes rockfall volume 200 4500 m3 length of magma column 120 210 m diameter of pipe connecting the halemaumau pit crater to the subjacent dike system 6 m average thickness of the two underlying dikes 3 6 m and effective magma viscosity 30 210 pa s most rockfalls occur during episodes of sustained deflation of the kilauea summit the mass loss rate in the shallow magmatic system is estimated to be 1400 15 000 kg s 1 based on measurements of the temporal variation of vlp period in the two large rockfalls that occurred on 29 august 2012

tilt change recorded by broadband seismometer prior to small phreatic explosion of meakan dake volcano hokkaido japan 1 we discovered an anomalous very long period vlp signal duration about 60 s in the broadband seismic record of the precursory swarm of a small phreatic explosion at the meakan dake volcano hokkaido japan in 2006 this signal was masked by a short period tremor in the original velocity waveform but a considerable dc step appeared in the displacement trace since such a step results from a tilt change we interpreted the observed trace as being a combination of rotational tilt and translational displacement motions the apparent displacement step in the vlp signal indicates subsidence of the summit crater owing to limited data we attempted deflating the mogi source and simulating the seismic record including both motions when only rotational motion is considered the simulated waveform explains well the general features of the observed trace however the combined trace has incompatible phases suggesting that a more complicated source process should be considered

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

very long period pulses at asama volcano central japan inferred from dense seismic observations summary we observed seismic events consisting of several one sided velocity pulses with durations of 5 30 s hereafter called very long period or vlp pulses using up to 14 broad band seismometers installed near the summit area of asama volcano japan particle motions do not point to a single source location despite their rectilinearities suggesting a non isotropic source mechanism together with path effect we conducted moment tensor inversion analyses for these events using the green s functions of not only translational motions but also of tilt motions the best fitting source locations are located north of the crater centre at depths of 100 150 m below the crater bottom the principal value ratios of moment tensor solutions can be approximated as 5 3 2 which is indicative of a combination of a tensile crack and a cylinder with the strike and dip angle of the crack both being nearly 70 and symmetry axis of the cylinder being inclined by nearly 30 from the vertical the time histories of moment tensors are indicative of an initial sudden pressurization and subsequent gradual depressurization at the source region we sought to model vlp pulses at asama volcano by considering the inflow and outflow of gas at the source cavity compensated by boiling in another deeper reservoir

dissection of a composite volcanic earthquake at santiaguito guatemala 1 volcano earthquake sources associated with eruptions at santiaguito volcano in guatemala are complex rock fracture fluid flow and gas expansion occur at variable time scales and induce superposed ground motions including both static and dynamic deformation and atmospheric pressure disturbances dissection of this composite event is facilitated through extra seismic observations such as infrasound geodetic and visual monitoring multi parametric investigation of an eruptive event on jan 4th 2009 reveals increased degassing apparent as both geodetic tilt and harmonic seismo infrasonic tremor preceding an explosive event the explosive event itself entails surface dome uplift multiple eruptive pulses and subsequent re equilibration of the volcanic edifice manifested in derived tilt we report here on an integrated approach to discerning the physical processes at the actively effusing and exploding santiaguito volcano and describe the composite earthquake that occurs here

non plane geometries of seismic surface wavefields and their implications for regional surface wave tomography summary seismic surface waves exhibit much more complicated wavefields than is commonly assumed we are led to this conclusion after analysing 90 teleseismic events recorded at on average eight broad band stations in southern germany large amplitude and phase fluctuations across the network are observed which as we show are definitely not due to instrument response or calibration problems in order to give an impression of how surface wavefields may look in reality we fit wavefields to the observed network data using basis wavefields derived from hermite gaussian functions we show both amplitude and phase distributions of several events synthetic wavefields generated by acoustic finite difference computations in a random medium with realistic correlation length and rms velocity fluctuations support the interpretation that most of the observed wavefield anomalies have accumulated on the path of the wave from the source to the network even if no lateral heterogeneities existed in the region of the network the large scale features of the observed wavefields would remain nearly unaltered we also model the synthetic wavefields using hermite gaussian wavefields and achieve extremely good fits in view of the large anomalies of the wavefields we investigate their implications for the regional surface wave tomography in this method one infers regional structure from a set of measurements of phase traveltime between pairs of stations the basic assumption of the method is that the wavefield incident on the network be plane thus all observed phase traveltime anomalies are interpreted in terms of regional heterogeneous structure the consequence is a seemingly highly inconsistent data set we perform several tomographic experiments with realistic synthetic data sets our experiments indicate that regional surface wave tomography may work if there is an excellent coverage of paths crossing the region and if each path is sampled several times under realistic conditions that is on a sparse network with not much more than one velocity value per path the imaging power of surface wave tomography is very poor owing to the seeming inconsistency of the phase traveltimes variance reduction is generally low with an increasing number of traveltime data it further decreases while at the same time the imaging power increases the opposite behaviour is observed if the number of data is reduced variance reduction increases but imaging power decreases hence in connection with regional surface wave tomography high variance reduction indicates a lack of data rather than the goodness of reconstruction

sharp contrast in lithospheric structure across the sorgenfrei tornquist zone as inferred by rayleigh wave analysis of tor1 project data abstract this work is a part of the tor1 project 1996 1997 and is devoted to determining the lithospheric structure across the sorgenfrei tornquist zone in northern europe for the first time in europe a very dense seismic broadband array has offered the possibility of determining very sharp lateral variations in the structure of the lithosphere at small scales using surface wave analysis we measure phase velocities for rayleigh waves with periods ranging between 10 and 100 s both within arrays with apertures of 40 50 km small compared to the wavelength and along long profiles of at least 100 km dispersion curves are then inverted and shear wave velocity models down to the depth of 200 km are proposed we show that the sorgenfrei tornquist zone is a major tectonic feature within the whole lithosphere north east of this feature in sweden beneath the baltic shield no lithosphere asthenosphere boundary is observed to exist to depths of 200 km south west of the sorgenfrei tornquist zone beneath denmark we find a lithospheric thickness of 120 20 km the transition across the sorgenfrei tornquist zone is sharp and determined to be very steeply dipping to the south west we also demonstrate the existence of a sharp discontinuity between the lithospheres beneath denmark 120 20 km thick and beneath germany characterized by thicknesses of 50 10 km in the northernmost part and 100 20 km in the southwest this discontinuity is most likely related to the trans european fault at the surface

arrival angle anomalies across the usarray transportable array abstract we construct composite maps of surface wave arrival angle anomalies using clustered earthquakes and an array method for measuring wave front geometry this results in observations of arrival angles covering the entire footprint of the usarray transportable array during 2006 2010 bands of arrival angle deviations in the propagation direction indicate the presence of heterogeneous velocity structure both inside and outside of the array we compare the observed patterns to arrival angles predicted using two global tomographic models the mantle model s362ani and the surface wave dispersion model gdm52 we use both ray theory based prediction methods and measurements on synthetic data calculated using a spectral element method both models and all prediction methods produce similar mean arrival angles and long wavelength patterns of anomalies which are similar to the observations predicted short wavelength features generally do not agree with the observations the spectral element method produces some complexity that is not obtained using the ray theory based methods this predicted complexity is similar in character to the observed patterns but does not match them

surface wave dispersion and upper mantle structure beneath southern germany from joint inversion of network recorded teleseismic events we have determined the dispersion of fundamental mode rayleigh waves in southern germany in the frequency range 4 50 mhz by simultaneously inverting data from 66 teleseismic events recorded at a network of up to 9 broadband stations three different inversion experiments were performed determination of 1 isotropic phase velocity of 2 azimuthally anisotropic phase velocity assuming a plane wave traveling across the network and 3 isotropic phase velocity but now allowing for non plane properties of the wavefield in experiments 1 and 2 for each event amplitude phase and deviation from the great circle azimuth were estimated as well we have obtained remarkably stable results for phase velocity over the whole frequency range between 7 and 25 mhz azimuthal anisotropy is definitely below 0 5 percent below 7 and above 25 mhz we found up to 3 percent anisotropy but with negligible variance reduction compared to the isotropic inversion experiment 1 admitting non plane wavefields in the inversion still yields nearly identical phase velocities on inversion of the phase velocity curve in terms of shear wave velocity we obtained a rather shallow asthenosphere with minimum s of 4 28 km s at about 130 km depth covered by a thin lid with s of 4 63 km s