seismic imaging of subduction zone metamorphism combined analysis of high resolution seismic images of the alaska and cascadia subduction zones reveals where metamorphic fl uids are released both images show the subducted oceanic crust as a dipping low velocity layer with a clear termination depth however in alaska the crust is thicker 15 20 km compared to 8 km and terminates at greater depth 120 km com pared to 40 km than in cascadia based on metamorphic reaction estimates and geodynamic models we demonstrate that the termination depth corresponds to eclogitization of the crust triggered by dehydration of water bearing minerals and that the location of this reaction is dependent on the thermal structure of the subducted slab

teleseismic waveform complexities caused by near trench structures and their impacts on earthquake source study application to the 2015 illapel aftershocks central chile

a threshold based earthquake early warning system for offshore events in southern iberia the south of the iberian peninsula is situated at the convergence of the eurasian and african plates this region experiences large earthquakes with long separation in time the best known of which was the great 1755 lisbon earthquake which occurred sw of san vicente cape sw iberian peninsula the high risk of damaging earthquakes has recently led carranzaet al geophys res lett 40 2013 to investigate the feasibility of an eews in this region analysis of the geometry for the iberian seismic networks and the san vicente cape area led the authors to conclude that a threshold based approach which would not require real time location of the earthquake might be the best option for an eews in sw iberia in this work we investigate this hypothesis and propose a new eew approach that extends standard p wave threshold based single station analysis to the whole network the proposed method enables real time estimation of the potential damage at stations that are triggered by p waves and those which are not triggered with the advantage of greater lead times for release of alerts results of tests made with synthetic data mimicking the scenario of the great 1755 lisbon earthquake and those conducted by applying the new approach to available recordings indicate that an eew estimation of the potential damage associated with an event in the san vicente cape area can be obtained for a very large part of the iberian peninsula

on the estimation of seismic intensity in earthquake early warning systems 1 the infamous tokai earthquake which by some accounts is overdue is expected to be a magnitude 8 event that will cause unprecedented damage in regions of japan to mitigate hazards from large earthquakes in japan an earthquake early warning eew system was developed that is able to determine hypocentral locations from p arrival data within a few seconds and then transmit this information before the onset of large ground motions from the later arrival of s waves we introduced a new source parameter for seismic intensity magnitude that can be estimated from the real time p wave data during the early stages of fault rupture for most earthquakes m 6 5 the use of this parameter results in a significant improvement in the uncertainty in the estimated seismic intensity compared to estimates derived from earthquake magnitude a pre established relation between the p and s wave seismic intensity therefore enables an eew system to issue a rapid and reasonably reliable prediction of the amount of ground shaking that may be expected from the damaging s waves

using τc to estimate magnitude for earthquake early warning and effects of near field terms 1 this paper analyzes strong motion records of 24 large earthquakes to investigate the relationship between c the period parameter of the first motion and moment magnitude the records of some of the large magnitude events very close to the source include large near field terms therefore if we include the data with large near field terms we may overestimate the final size of the magnitude we identified records with large near field terms and did not include these data in processing the records to compute c for each event our analysis shows that the value of c is between the earthquake corner period and the period determined by the record duration 0 if the magnitude is less than 6 c closely approximates the corner period whereas c for larger earthquakes depends on the rupture process and location of asperity c for large earthquakes provides a lower bound on the event magnitude and approaches the corner period if a longer record is used we also propose a method to classify the records with and without large near field terms if the peak displacement amplitude for the first 3 s pd3 exceeds 1 cm and c exceeds 2 s the record is more likely to include large near field terms for the purpose of quick onsite warnings stations observing large near field terms provide valuable information large near field terms can be observed only if the magnitude is large and the epicentral distance is small therefore if the displacement exceeds a threshold e g pd 0 5 cm the ground motion at the site would likely become very large this criterion will help to issue warnings to the blind zone which is the region where there is insufficient time to issue a warning before the strong shaking arrives

probing depth and lateral variations of upper mantle seismic anisotropy from full waveform inversion of teleseismic body waves we present an extension of the regional full waveform inversion method to image seismic anisotropy in the lithosphere and asthenosphere from teleseismic p and s waveforms the models are parameterized in terms of density and the 21 elastic coefficients of the fourth order elasticity tensor the inversion method makes no a priori assumptions on the symmetry class or on the orientation of the symmetry axes instead the elasticity tensors in the final models are decomposed with the projection method of browaeys chevrot 2004 this method allows us to determine the orientation of the symmetry axes and extract the contributions of each symmetry class e g hexagonal symmetry from simple synthetic experiments we demonstrate that our full waveform inversion method is able to image complex three dimensional anisotropic structures in particular the method is able to almost perfectly recover layered anisotropic models which produce very small apparent shear wave splitting an extremely challenging case we attribute this success to the joint exploitation of both p and s teleseismic waves which constrain different parts of the elasticity tensor another key ingredient is the preconditioning of the gradient with an approximate inverse hessian computed with scattering integrals the inverse hessian is crucial to correct for the effects of the uneven mostly vertical illumination of teleseismic acquisitions 2 beller et al

imaging the lithosphere beneath ne tibet teleseismic p and s body wave tomography incorporating surface wave starting models the northeastern margin of the tibetan plateau which includes the qiangtang and songpan ganzi terranes as well as the kunlun shan and the qaidam basin continues to deform in response to the ongoing india eurasia collision to test competing hypotheses concerning the mechanisms for this deformation we assembled a high quality data set of approximately 14 000 p and 4000 s wave arrival times from earthquakes at teleseismic distances from the international deep profiling of tibet and the himalaya phase iv broad band seismometer deployments we analyse these arrival times to determine tomographic images of p and s wave velocities in the upper mantle beneath this part of the plateau to account for the effects of major heterogeneity in crustal and uppermost mantle wave velocities in tibet we use recent surface wave models to construct a starting model for our teleseismic body wave inversion we compare the results from our model with those from simpler starting models and find that while the reduction in residuals and results for deep structure are similar between models the results for shallow structure are different checkerboard tests indicate that features of 125 km length scale are reliably imaged throughout the study region using synthetic tests we show that the best recovery is below 300 km and that broad variations in shallow structure can also be recovered we also find that significant smearing can occur especially at the edges of the model we observe a shallow dipping seismically fast structure at depths of 140 240 km which dies out gradually between 33 n and 35 n based on the lateral continuity of this structure from the surface waves we interpret it as indian lithosphere alternatively the entire area could be thickened by pure shear or the northern part could be an underthrust lhasa terrane lithospheric slab with only the southern part from india we see a deep fast wave velocity anomaly below 300 km that is consistent with receiver function observations of a thickened transition zone and could be a fragment of oceanic lithosphere in ne tibet it appears to be disconnected from faster wave velocities above i e it is not downwelling or subducting here our models corroborate results of previous work which imaged a relatively slow wave velocity region below the kunlun shan and northern songpan ganzi terrane which is difficult to reconcile with the hypothesis of southward directed continental subduction at the northern margin wave velocities in the shallow mantle beneath the qaidam basin are faster than normal and more so in the east than the west

multiple seismic reflectors in earth s lowermost mantle the modern view of earth s lowermost mantle considers a d region of enhanced seismologically inferred heterogeneity bounded by the core mantle boundary and an interface some 150 300 km above it with the latter often attributed to the postperovskite phase transition in mgsio3 seismic exploration of earth s deep interior suggests however that this view needs modification so called scs and skks waves which probe the lowermost mantle from above and below respectively reveal multiple reflectors beneath central america and east asia two areas known for subduction of oceanic plates deep into earth s mantle this observation is inconsistent with expectations from a thermal response of a single isochemical postperovskite transition but some of the newly observed structures can be explained with postperovskite transitions in differentiated slab materials our results imply that the lowermost mantle is more complex than hitherto thought and that interfaces and compositional heterogeneity occur beyond the d region sensu stricto

adjoint tomography of the southern california crust using an inversion strategy based on adjoint methods we developed a three dimensional seismological model of the southern california crust the resulting model involved 16 tomographic iterations which required 6800 wavefield simulations and a total of 0 8 million central processing unit hours the new crustal model reveals strong heterogeneity including local changes of 30 with respect to the initial three dimensional model provided by the southern california earthquake center the model illuminates shallow features such as sedimentary basins and compositional contrasts across faults it also reveals crustal features at depth that aid in the tectonic reconstruction of southern california such as subduction captured oceanic crustal fragments the new model enables more realistic and accurate assessments of seismic hazard

a 3 d spectral element and frequency wave number hybrid method for high resolution seismic array imaging we present a three dimensional 3 d hybrid method that interfaces the spectral element method sem with the frequency wave number fk technique to model the propagation of teleseismic plane waves beneath seismic arrays the accuracy of the resulting 3 d sem fk hybrid method is benchmarked against semianalytical fk solutions for 1 d models the accuracy of 2 5 d modeling based on 2 d sem fk hybrid method is also investigated through comparisons to this 3 d hybrid method synthetic examples for structural models of the alaska subduction zone and the central tibet crust show that this method is capable of accurately capturing interactions between incident plane waves and local heterogeneities this hybrid method presents an essential tool for the receiver function and scattering imaging community to verify and further improve their techniques these numerical examples also show the promising future of the 3 d sem fk hybrid method in high resolution regional seismic imaging based on waveform inversions of converted scattered waves recorded by seismic array

reply to comment by p rydelek et al on earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records 1 based on the analysis of mediterranean near source strong motion records zollo et al 2006 hereinafter referred to as zln showed that peak displacement amplitudes of initial pand s wave seismic signals scales with the earthquake size in the moment magnitude range 4 6 1 9 in figure 1 we report data distribution vs magnitude and hypocentral distance note that the distance distribution of analyzed events for japan figure 1 is clearly different from that for the mediterranean med earthquakes given by zln whereas most of med records occur at an hd 40 km 10 at odds with rwh we did not apply any cut off at m 5 5 on hypocentral distance for small and moderate events indeed this may introduce a bias on the estimation of attenuation law parameters retrieved from both small and large earthquakes records we follow the zln procedure involving among others sensitivity correction p and s phase identification double integration filtering in a frequency band 0 075 3 hz peaks are read on the modulus of displacement expressed in meters starting from the pwave and s wave picked arrivals we measure peaks within a 2 second window for the p arrival we also test the method with 4 second windows 11 the distance attenuation effect is corrected for by assuming a simple log linear model wu and zhao 2006 zln the amplitudes are normalized to a reference distance of 10 km i e the same as for zln in the mediterranean study to facilitate comparison though rwh show data normalized at a distance of 20 km zln figures 2a and 2b the use of a different normalization distance does not change the slope of the log peak vs magnitude relationships and thus does not alter the graphical interpretation 12 in figure 2 we show the relation between the logarithm of distance normalized peak displacement for p and s waves in different time windows vs final magnitude of the events following zln statistical significance was geophysical research letters vol 34 l20303 doi 10 1029 2007gl030560 2007 click here for full article

regional mapping of the crustal structure in southern california from receiver functions lateral variations of the crustal structure in southern california are determined from receiver function rf studies using data from the southern california seismic network broadband stations and los angeles regional seismic experiment surveys the results include crustal thickness estimates at the stations themselves and where possible cross sections are drawn the large scale moho depth variation pattern generally correlates well with the current status of the mesozoic batholith deep moho of 35 39 km is observed beneath the western peninsula ranges sierra nevada and san bernardino mountains where the batholith is relatively intact and shallow moho of 26 32 km is observed in the mojave desert where the batholith is highly deformed and disrupted high resolution lateral variations of the crustal structure for individual geographic provinces are investigated and distinctive features are identified the crustal structure is strongly heterogeneous beneath the central transverse ranges and deep moho of 36 39 km is locally observed beneath several station groups in the western san gabriel mountains moho is relatively flat and smooth beneath the western mojave desert but gets shallower and complicated to the east anomalous rfs are observed at two stations in the eastern mojave desert where a moho step of 8 10 km is found between the nw and se back azimuthal groups of station dan in the fenner valley asymmetric extension of the salton trough is inferred from the moho geometry depth extension of several major faults such as the san andreas fault and san gabriel fault to the moho is inferred

atmospheric storm triggered and intensified by geodynamics case studies from andaman sea and bay of bengal region in the indian ocean the study analyses the possible connection between the onset of cyclone and volcano tectonic seismicity in the andaman region the historical data of the major volcanic seismic and atmospheric events from the region show that several of the geodynamic activities were followed by severe atmospheric disturbances over the region in this study we consider the case of three recent cyclones phailin hudhud and nilam that either originated or were intensified over the andaman sea and bay of bengal and examine their correlation with the volcano tectonic seismic events during the cyclone occurrence the zenith total delay ztd time series derived from global positioning system data from the pbr2 station on andaman island overlapping with the period of the cyclone occurrence were examined to distinguish the onset and intensification of the atmospheric events the comparison of the sharp changes in ztd associated with the cyclone and the seismic events during the period indicates that the atmospheric changes almost coincide or follow the geodynamic activity our study illustrates that volcano tectonics of the region plays a role in the triggering of atmospheric disturbances

imaging the upper mantle transition zone with a generalized radon transform of ss precursors we demonstrate the feasibility of using inverse scattering for high resolution imaging of discontinuities in the upper mantle beneath oceanic regions far from sources and receivers using broadband wavefield observations consisting of ss and its precursors the generalized radon transform grt that we developed for this purpose detects in the broadband data signals due to scattering from elasticity contrasts in earth s mantle synthetic tests with realistic source receiver distributions demonstrate that the grt is able to detect and image deep mantle interfaces even in the presence of noise depth phases ghosts phase conversions and multiples generated by reverberation within the transition zone as a proof of concept we apply the grt to 50 000 broadband seismograms to delineate interfaces in the depth range from 300 to 1000 km beneath the northwest pacific we account for smooth 3d mantle heterogeneity using first order perturbation theory and independently obtained global tomography models the preliminary results reveal laterally continuous but undulating scatter zones near 410 and 660 km depth and a weaker broader and more complex structure near 520 km depth the images also suggest the presence of multiple laterally intermittent interfaces near 350 km and between 800 and 1000 km depth that is above and below the transition zone sensu stricto filtering of the data we consider four pass bands 20 50 s 10 50 s 5 50 s and 2 50 s reveals a prominent frequency dependence of the magnitude width and complexity of the interfaces in particular of the scatter zone near 520 km depth such dependencies may put important constraints on the mineralogy and phase chemistry of the transition zone

reverse time migration based reflection tomography using teleseismic free surface multiples converted and multiply reflected phases from teleseismic events are routinely used to create structural images of the crust mantle boundary moho and the elasticity contrasts within the crust and upper mantle the accuracy of these images is to a large extent determined by the background velocity model used to propagate these phases to depth in order to improve estimates of 3 d velocity variations and hence improve imaging we develop a method of reverse time migration based reflection tomography for use with wavefields from teleseismic earthquakes recorded at broad band seismograph arrays reflection tomography makes use of data redundancy that is the ability to generate numerous structural images of the subsurface with different parts of the wavefield in exploration seismology where it is known as migration velocity analysis reflection tomography typically involves the generation of an extended image e g offsetor angle gathers and the fitness of the background model is evaluated through the application of image domain annihilators in regional scale passive source seismology however annihilation based methods are inadequate because the sparse and irregular distribution of teleseismic sources is not likely to produce illumination over a sufficient range of angles to overcome this problem we turn towards a source indexed moveout scheme instead of extended image annihilation we determine the success of the tomographic velocity model by cross correlating images produced with multiply scattered waves from different teleseismic sources the optimal velocity model is the one that minimizes correlation power between windowed images away from zero depth shift we base our inversion scheme on the seismic adjoint method and a conjugate gradient solver for each image pair the update direction is determined by correlations between downgoing wavefields with upgoing adjoint wavefields for both images the sensitivity kernels used in this method is similar to those found in other forms of adjoint tomography but their shapes are controlled by the spatial distribution of the error function we present the method and a proof of concept with 2 d synthetic data

an automatic processing system for broadcasting earthquake alarms in japan most of the damage caused by large earthquakes is concentrated within areas less than about 100 km from the focal regions we have developed an earthquake alarm system that determines earthquake parameters within a few seconds of the p wave s arrival at the closest station and then transmits the earthquake information before the s wave arrival in areas of possible serious earthquake damage since an earthquake alarm system requires the determination of reliable earthquake parameters as quickly as possible it is unreasonable to wait until waveform data from numerous stations have been collected for analysis for this reason we have developed a novel method of determining the hypocentral location by using the arrival times for only a few stations as well as the lack of p wave arrivals at other stations at a given time the use of not yet arrived data makes it possible not only to determine reliable hypocenter parameters within a few seconds but also to detect erroneous arrival time readings and remove them automatically since the available waveform data increases with time the system was designed to redetermine earthquake parameters every second our method was deployed in a real time system starting in july 2002 the real time system locates 10 20 events per day which includes a few felt earthquakes occurring in and around japan it was shown from the waveform data for about 100 felt earthquakes that almost all the events except those far from the network could be located within a few seconds when most of seismic energy has not even arrived at some stations close by we recently started widespread broadcasting of earthquake information in real time by using a satellite transmission system

predicting head cut erosion and migration in concentrated flows typical of upland areas 1 soil erosion due to head cut development and migration can devastate agricultural lands yet current prediction technology does not address this important erosion process here an analytical model of this erosional phenomenon is presented realistic physically based approximations to the laws governing mass momentum and energy transfer in the neighborhood of the scour hole result in closed form predictive algorithms for the magnitude of the plunge pool erosion and the rate of head cut migration the model introduces a special treatment of nonventilated overfall conditions is limited to homogeneous unbounded soil layers and is validated by available experimental measurements

teleseismic shot profile migration the shot profile migration approach of wave equation migration generates subsurface images using the interferometric principle of crosscorrelating two passive wavefields these wavefields are typically a source wavefield containing energy from an excited source and a receiver wavefield comprised of scattered source wavefield energy by the discontinuous earth structure shot profile migration can be recast as a novel way of imaging the earth s lithosphere using teleseismic wavefield data where the source wavefield is the directly arriving wavefront and the receiver wavefield is the following wavefield coda we demonstrate that the shot profile technique can be tailored to suit teleseismic acquisition geometry and wavefields assuming an acoustic framework and 2 5d experimental geometry we develop procedures that enable kinematic and structural imaging migration using both transmission and free surface reflected passive wavefields experiments with synthetic data demonstrate the method s applicability a

seismic migration processing of p sv converted phases for mantle discontinuity structure beneath the snake river plain western united states we experiment with backprojection migration processing of teleseismic receiver functions from the snake river plain srp broadband seismic experiment previous analyses of data from this experiment have used a common midpoint cmp stacking approach a method widely applied for analysis of p sv converted phases receiver functions to obtain high resolution imaging of upper mantle discontinuities the cmp technique assumes that all p sv conversions are produced by flat lying structures and may not properly image dipping curved or laterally discontinuous interfaces in this paper we adopt a backprojection migration scheme to solve for an array of point scatterers that best produces the large suite of observed receiver functions we first perform synthetic experiments that illustrate the potential improvement of migration processing over cmp stacks application of the migration processing to the srp data set shows most of the major features as in the original cmp work but with a weaker 410 km discontinuity and a more intermittent discontinuity at 250 km apparent depth random resampling tests are also performed to assess the robustness of subtle features in our discontinuity images these tests show that a 20 km elevation of the 660 km discontinuity directly beneath the snake river plain is robust but that the variations in 410 km discontinuity topography that we observe are not stable upon resampling bright spots near 250 km apparent depth are robust upon resampling but interpretation of these features is complicated by possible sidelobe artifacts from topside moho reverberations

comment on earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records by aldo zollo maria lancieri and stefan nielsen an early warning system should determine the loca tion and magnitude of an earthquake as rapidly as possiblein order to broadcast an alarm to regions that will undergosevere ground shaking it was recently claimed by zollo etal 2006 that earthquake size could be determined fromonly the first 2 seconds of p or s wave strong motion data this represents a fraction of the rupture time for larger m 7 events using this relatively short amount of data themethod of analysis was to find the peak ground displace ment pgd which was reported to scale with earthquakemagnitude such rapid information would play an importantand much needed role in an earthquake early warning eew system here we perform a similar analysis onstrong motion data from the kik net and k net arrays injapan and find no compelling evidence that the peak grounddisplacement during the first couple of seconds of p wave isrelated to the eventual size of a large earthquake

jet and hydraulic jump near bed stresses below a horseshoe waterfall 1 horseshoe waterfalls are a common but unexplained feature of bedrock rivers as a step toward understanding their geomorphology a six component force torque sensor was used to evaluate clear water scour mechanisms in a 0 91 m broad crested horseshoe waterfall built into a 2 75 m wide flume to measure longitudinal lateral and temporal profiles of the near bed spatially averaged stress vector jet impact caused moderate near bed stress downstream of the impact point the stress vector shifted into a much more forceful upthrust with peak stress beyond the boil crest instantaneous fluctuations in near bed lift exceeded drag by 5 10 times and occurred over a wider range of frequencies suggesting a larger role for particle entrainment predictions of bed stress significantly underestimated actual conditions these results show that horseshoe waterfalls have an extended region of high scour along their centerline corresponding with the three dimensional convergent dynamics associated with both jet impact and jump enhanced lift fluctuations

a parametric analysis of two dimensional elastic full waveform inversion of teleseismic data for lithospheric imaging the development of dense networks of broad band seismographs makes teleseismic data amenable to full waveform inversion fwi methods for high resolution lithospheric imaging compared to scattered field migration fwi seeks to involve the full seismic wavefield in the inversion we present a parametric analysis of 2 d frequency domain fwi in the framework of lithospheric imaging from teleseismic data to identify the main factors that impact on the quality of the reconstructed compressional p wave and shear s wave speed models compared to controlled source seismology the main adaptation of fwi to teleseismic configuration consists of the implementation with a scattered filed formulation of plane wave sources that impinge on the base of the lithospheric target located below the receiver network at an arbitrary incidence angle seismic modelling is performed with a hp adaptive discontinuous galerkin method on unstructured triangular mesh a quasi newton inversion algorithm provides an approximate accounting for the hessian operator which contributes to reduce the footprint of the coarse acquisition geometry in the imaging a versatile algorithm to compute the gradient of the misfit function with the adjoint state method allows for abstraction between the forward problem operators and the meshes that are during seismic modelling and inversion respectively an approximate correction for obliquity is derived for future application to real teleseismic data under the two dimension approximation comparisons between the characteristic scales involved in exploration geophysics and in teleseismic seismology suggest that the resolution gain provided by full waveform technologies should be of the same order of magnitude for both applications we first show the importance of the surface reflected wavefield to dramatically improve the resolving power of fwi by combining tomography like and migration like imaging through the incorporation of the forward scattered and the backscattered wavefields in the inversion the resolution of fwi is assessed through checkerboard tests and confirms a resolution of the order of the wavelength for both the p and s speeds when the full wavefield is incorporated in the inversion secondly we show that computationally efficient strategies which consist of decimating the number of frequency components involved in the inversion do not apply to teleseismic acquisitions because the scattering angle bandwidth sampled by plane wave sources can be narrow and coarsely sampled compared to that provided by dense profiles of point sources in exploration seismology the waveform inversion is less sensitive to the band of incidence angles spanned by the plane wave sources and to the sampling of this band however the deficit of vertically propagating plane waves hampers the vertical resolution of planar layers aliasing artefacts created by coarse arrays of receivers are illustrated we show how taking into account the hessian in the inversion and the suitable management of frequencies in the inversion help to mitigate these artefacts acceptable reconstructions are shown for both the p and s wave speeds for a receiver spacing of up to 20 km in the 0 1 0 4 hz frequency range building a reliable initial model for fwi is a highly non linear problem in exploration seismology we show how the low frequency content of the teleseismic sources allow us to build accurate p and s wave speed models starting from simple vertical gradient velocity models all of these results are derived using a 2 d realistic synthetic experiment that was performed with noise free data most of conclusions of this parametric study should apply in three dimensions the impact of noise and the footprint of other experimental parameters such as the estimation of the temporal plane wave signature and the estimation of the incidence angle of the impinging plane waves need however to be assessed in the future

a data adaptive multiscale approach of finite frequency traveltime tomography with special reference to p and s wave data from central tibet 1 we discuss an innovation in traveltime tomography that combines wavelet based multiscale parameterization and finite frequency theory to solve two outstanding issues that inevitably arise from uneven source station distributions and from the three dimensional 3 d nature of wavefront healing how to objectively address the intrinsically multiscale nature of data coverage while simultaneously maintain model resolution at each scale level we apply the new integrated methodology to investigate 3 d variations of p and s wave speeds lnvp and lnvs beneath the himalayan tibetan orogen in particular we are able to constrain variations in the poisson s ratio via ln vp vs the formulation is naturally data adaptive resolving features at each scale only if the required data converge is available the very first long wavelength feature that emerges is a clear anomaly of high lnv that extends over more than 500 km beyond the northern edge of the lhasa terrane at places farther northward a strong negative anomaly underlies the region where recent volcanism occurs in northern tibet regions of negative ln vp vs delineate a slab like subhorizontal feature concentrated between depths of 100 250 km such characteristics are consistent with the notion that chemically refractory and therefore buoyant mantle lithosphere of the indian shield greater india has advanced subhorizontally northward far beyond the surficial bangong nujiang suture in the crust two isolated regions of low lnv each extending to depths near 100 km occur along the lunggar and the yadong gulu active rifts in southern tibet deep penetrating rifts imply that only a limited amount of horizontal displacement is being accommodated on subvertical structures

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

experiments and modeling of head cut migration in stratified soils 1 a two dimensional model is developed to predict head cut migration rate for the specific case of a relatively erosion resistant soil layer overlying a deep relatively erosive base soil for this geometry head cut migration can occur as a series of discrete mass failures of the surface layer caused by undercutting in a plunge pool formed immediately downstream the length scale of one failure episode is modeled as a cantilevered slab failing in bending the timescale for each failure episode is controlled by the rate and geometry of base layer scour which is modeled independently of cantilevered slab properties an integration of the two model components for the case of steady flow and uniform soil properties predicts linear upstream head cut migration with time occurring in discrete steps bounded by successive mass failure events the model is calibrated and tested in a series of flume experiments representing ideal conditions of different initial geometries and flow conditions head cut migration occurred by the proposed mechanism in a nearly linear rate average error between the observed and predicted retreat rate is 40 most of this error is attributable to prediction of the scour hole shape

real time seismic warning with a two station subarray one of the most basic problems in seismology is earthquake location in particular the ability to quickly locate a large potentially devastating earthquake is of fundamental importance in a real time warning system where speed is a key factor in determining the level of success of such systems we have developed a simple method that uses only the two earliest p wave arrival times in a seismic array assuming a simple velocity model these arrivals are used to construct a hyperbolic curve on which the approximate epicenter of the earthquake is expected to lie epicentral location along this hyperbola is further constrained by using the fact that the p waves arriving at the other stations in the array are not first arrivals when applied to p wave seismic data from the hector mine earthquake in california and a smaller event in the central united states model results show agreement with actual earthquake locations although there is an inherent uncertainty in the subarray method of locating large earthquakes this may be an acceptable trade off in an early warning system in view of the time a few to tens of seconds saved by not waiting for other p arrivals whereas the main goal of this report is to present the location method we also show that the station closest to the hector mine earthquake had recorded about 0 3 and 1 mm of ground motion within 2 and 3 sec respectively of the arrival of the p waves thus indicating that a large event had occurred manuscript received 18 september 2003

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

beyond receiver functions passive source reverse time migration and inverse scattering of converted waves 1 we present a wave equation prestack depth migration to image crust and mantle structures using multi component earthquake data recorded at dense seismograph arrays transmittedp and swaves recorded on the surface are back propagated using an elastic wave equation solver the wave modes are separated after the reverse time continuation of the wavefield from the surface and subjected to a cross correlation type imaging condition forming an inverse scattering transform reverse time migration rtm does not make assumptions about the presence or properties of interfaces notably it does not assume that interfaces are locally horizontal with synthetic experiments and different background models we show that passive source rtm can reconstruct dipping and vertically offset interfaces even in the presence of complex wave phenomena such as caustics and point diffraction and that its performance is superior to traditional receiver function analysis e g common conversion point ccp stacking in complex geological environments

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

cybershake derived ground motion prediction models for the los angeles region with application to earthquake early warning real time applications such as earthquake early warning eew typically use empirical ground motion prediction equations gmpes along with event magnitude and source to site distances to estimate expected shaking levels in this simplified approach effects due to finite fault geometry directivity and site and basin response are often generalized which may lead to a significant under or overestimation of shaking from large earthquakes m 6 5 in some locations for enhanced site specific ground motion predictions considering 3 d wave propagation effects we develop support vector regression svr models from the scec cybershake low frequency 415 000 finite fault rupture scenarios 6 5 m 8 5 for southern california defined in ucerf 2 0 we use cybershake to demonstrate the application of synthetic waveform data to eew as a proof of concept being aware that these simulations are not yet fully validated and might not appropriately sample the range of rupture uncertainty our regression models predict the maximum and the temporal evolution of instrumental intensity mmi at 71 selected test sites using only the hypocentre magnitude and rupture ratio which characterizes uni and bilateral rupture propagation our regression approach is completely data driven where here the cybershake simulations are considered data and does not enforce pre defined functional forms or dependencies among input parameters the models were established from a subset 20 per cent of cybershake simulations but can explain mmi values of all 400 k rupture scenarios with a standard deviation of about 0 4 intensity units we apply our models to determine threshold magnitudes and warning times for various active faults in southern california that earthquakes need to exceed to cause at least moderate strong or very strong shaking in the los angeles la basin these thresholds are used to construct a simple and robust eew algorithm to declare a warning the algorithm only needs to locate the earthquake and to verify that the corresponding magnitude threshold is exceeded the models predict that a relatively moderate m6 5 7 earthquake along the palos verdes newport inglewood rose canyon elsinore or san jacinto faults with a rupture propagating towards la could cause very strong to severe shaking in the la basin however warning times for these events could exceed 30 s

shear wave birefringence and current configuration of converging lithosphere under tibet article i nfo new data from west central tibet show that birefringence of s waves has two pronounced increases in magnitude toward the hinterland null birefringence persists to about 75 km north of the indus yarlung suture iys between the indian shield and the lhasa terrane of southern tibet a second rapid increase occurs about 100 km farther north of the bangong nujiang sutures between the lhasa terrane and the qiangtang terrane in central tibet the latter feature is consistently observed along three long transects that collectively span a lateral orogen parallel distance of about 600 km and is likely to mark the northern leading edge of sub horizontally advancing mantle lithosphere of the indian shield the greater india an interpretation consistent with the latest results of finite frequency tomography using both p and s wave travel times previous results of modeling gravity anomalies and a host of other seismic observations similarly complementary constraints indicate that the sudden onset of significant birefringence north of the iys is likely to be the southern termination of eurasian mantle lithosphere curiously the shortest of three transects showed null birefringence through much of the lhasa terrane a pattern inconsistent with those of he isotopes and gravity

stable width and depth of gravel bed rivers with cohesive banks an analytical model is developed to determine the influence of the bank stability on the stable width and depth of alluvial gravel bed rivers with cohesive banks the formulation of the model is based on the assumption that the stable width corresponds with an optimum condition that is equivalent to the maximum bed load transporting capacity the optimum condition develops when the channel banks are at their limiting stability with respect to either mass failure or fluvial erosion two basic channel types are identified bank height and bank shear constrained mass failure stability is estimated using a simple total stress approach a method for estimating the critical bank shear stress based on model calibration is proposed analysis of field data indicates that the effect of the bank vegetation on bank stability can be expressed in terms of the critical bank shear stress the average critical bank shear stress value calculated for riverbanks covered by vegetation with well developed root networks was fo

a scattered wave image of subduction beneath the transverse ranges over 5600 short period recordings of teleseismic events were used to create deterministic maps of p wave scatterers in the upper mantle beneath southern california between depths of 50 and 200 kilometers the southern flank of the slab subducting beneath the transverse ranges is marked by strong scattering the marked scattering indicates that the edge of the slab is a sharp thermal boundary such a boundary could be produced by slab shearing or small scale convection in the surrounding mantle the northern limb of the slab is not a strong scatterer consistent with thicker lithosphere north of the transverse ranges

a new trigger criterion for improved real time performance of onsite earthquake early warning in southern california we have implemented and tested an algorithm for onsite earthquake early warning eew in california using the infrastructure of the southern california seismic network scsn the algorithm relies on two parameters derived from the initial 3 sec of p waveform data at a single seismic sensor period parameter c and high pass filtered displacement amplitude p d previous studies have determined empirical relationships between c and the moment magnitude m w of an earthquake and between p d and the peak ground velocity pgv at the site of observation in 2007 seven local earthquakes in southern california with 4 0 m l 4 7 have triggered the calculation of m w and pgv by the eew algorithm while the mean values of estimated parameters were in the expected range the scatter was large in particular for the smallest events during the same time period the eew algorithm produced a large number of false triggers due to low trigger thresholds to improve the real time performance of the onsite approach we have developed a new trigger criterion that is based on combinations of observed c and p d values this new criterion removes 97 of previous false triggers and leads to a significant reduction of the scatter in magnitude estimates for small earthquakes

small 660 km seismic discontinuity beneath tibet implies resting ground for detached lithosphere 1 using seismic profiles comprising of high resolution triplicate waveforms across apertures of over 1 000 km we show that because of high p wave speed vp near the bottom of the mantle transition zone the contrast in vp across the 660 km discontinuity beneath central tibet is small only about 70 of that beneath the northern indian shield this subhorizontal anomaly of high vp is most likely a remnant of detached mantle lithosphere that recently sank to depth thus providing key evidence for a direct connection between continental collision near the surface and deep seated dynamics in the mantle

three dimensional full waveform inversion of short period teleseismic wavefields based upon the sem dsm hybrid method we present a method for high resolution imaging of lithospheric structures based on full waveform inversion of teleseismic waveforms we model the propagation of seismic waves using our recently developed direct solution method spectral element method hybrid technique which allows us to simulate the propagation of short period teleseismic waves through a regional 3 d model we implement an iterative quasi newton method based upon the l bfgs algorithm where the gradient of the misfit function is computed using the adjoint state method compared to gradient or conjugate gradient methods the l bfgs algorithm has a much faster convergence rate we illustrate the potential of this method on a synthetic test case that consists of a crustal model with a crustal discontinuity at 25 km depth and a sharp moho jump this model contains short and long wavelength heterogeneities along the lateral and vertical directions the iterative inversion starts from a smooth 1 d model derived from the iasp91 reference earth model we invert both radial and vertical component waveforms starting from long period signals filtered at 10 s and gradually decreasing the cut off period down to 1 25 s this multiscale algorithm quickly converges towards a model that is very close to the true model in contrast to inversions involving short period waveforms only which always get trapped into a local minimum of the cost function

a wave equation migration method for receiver function imaging 2 application to the japan subduction zone 1 the newly developed wave equation poststack depth migration method for receiver function imaging is applied to study the subsurface structures of the japan subduction zone using the fundamental research on earthquakes and earth s interior anomalies freesia broadband data three profiles are chosen in the subsurface imaging two in northeast ne japan to study the subducting pacific plate and one in southwest sw japan to study the philippine sea plate the descending pacific plate in ne japan is well imaged within a depth range of 50 150 km the slab image exhibits a little more steeply dipping angle 32 in the south than in the north 27 although the general characteristics between the two profiles in ne japan are similar the imaged philippine sea plate in eastern sw japan in contrast exhibits a much shallower subduction angle 19 and is only identifiable at the uppermost depths of no more than 60 km synthetic tests indicate that the top 150 km of the migrated images of the pacific plate is well resolved by our seismic data but the resolution of deep part of the slab images becomes poor due to the limited data coverage synthetic tests also suggest that the breakdown of the philippine sea plate at shallow depths reflects the real structural features of the subduction zone rather than caused by insufficient coverage of data comparative studies on both synthetics and real data images show the possibility of retrieval of fine scale structures from high frequency contributions if high frequency noise can be effectively suppressed and a small bin size can be used in future studies the derived slab geometry and image feature also appear to have relatively weak dependence on overlying velocity structure the observed seismicity in the region confirms the geometries inferred from the migrated images for both subducting plates moreover the deep extent of the pacific plate image and the shallow breakdown of the philippine sea plate image are observed to correlate well with the depth extent of the seismicity beneath ne and sw japan such a correlation supports the inference that the specific appearance of slabs and intermediate depth earthquakes are a consequence of temperature dependent dehydration induced metamorphism occurring in the hydrated descending oceanic crust

magnitude estimation using the first three seconds p wave amplitude in earthquake early warning 1 pd is the peak amplitude of displacement in the first three seconds after the arrival of the p wave we investigated the attenuation of pd with the hypocentral distance r in southern california as a function of magnitude m and obtained the following relationship log pd 3 463 0 729 m 1 374 log r 0 305 given an earthquake location determined by the p wave arrival times at stations close to the epicenter this relationship can be used to define a so called pd magnitude of earthquakes our result shows that for earthquakes in southern california the pd magnitudes agree with the catalog magnitudes with a standard deviation of 0 18 for events less than magnitude 6 5 therefore pd is a robust measurement for estimating the magnitudes of earthquakes and has practical application in earthquake early warning systems citation wu y m and l zhao 2006 magnitude estimation using the first three seconds p wave amplitude in earthquake early warning geophys res lett 33 l16312 doi 10 1029 2006gl026871

fast determination of earthquake magnitude and fault extent from real time p wave recordings s u m m a r y this work is aimed at the automatic and fast characterization of the extended earthquake source through the progressive measurement of the p wave displacement amplitude along the recorded seismograms we propose a straightforward methodology to quickly characterize the earthquake magnitude and the expected length of the rupture and to provide an approximate estimate of the average stress drop to be used for earthquake earlywarning and rapid response purposes we test the methodology over a wide distance and magnitude range using a massive japan earthquake accelerogram data set our estimates of moment magnitude source duration length and stress drop are consistent with the ones obtained by using other techniques and analysing the whole seismic waveform in particular the retrieved source parameters follow a self similar constant stress drop scaling median value of stress drop 0 71 mpa for the m 9 0 2011 tohoku oki event both magnitude and length are underestimated due to limited available p wave time window ptws and to the low frequency cut off of analysed data we show that in a simulated real time mode about 1 2 seconds would be required for the source parameter determination of m 4 5 events 3 10 seconds for m 6 7 and 30 40 s for m 8 8 5 the proposed method can also provide a rapid evaluation of the average slip on the fault plane which can be used as an additional discriminant for tsunami potential associated to large magnitude earthquakes occurring offshore

development of gullies on the landscape a model of headcut retreat resulting from plunge pool erosion 1 head advance due to plunge pool erosion is a common process in gullies incising resistant soils a model of headcut retreat resulting from plunge pool erosion is developed and implemented in the channel hillslope integrated landscape development child model an existing three dimensional landscape evolution modeling framework the model estimates horizontal headcut retreat as a function of discharge height of the headcut upstream slope and relevant land surface and soil properties for soil erosion we analyze the sensitivity of headcut retreat to flow discharge upstream slope and surface roughness and headcut height child simulations indicate that headcut retreat is most significant in zones with either gentle slopes or large headcut heights model parameters have contrasting effects on the retreat rates depending on the size and depth of the pool beneath the headcut and upstream flow hydraulics making the process difficult to predict as a function of topographic thresholds and simple geomorphic transport laws

lithospheric imaging via teleseismic scattering tomography summary the coda of the teleseismic p phase consists largely of energy scattered by small inhomogeneities in the receiver side lithosphere given large collections of teleseismic data from dense permanent networks previous workers have successfully back propagated coda energy back to scattering source points using various kinematic migration schemes as well as by inverting using an inverse scattering radon transform approach under the born approximation seismic scattering is a linear process therefore it is possible to approach coda scattering as a linear waveform inversion problem mathematically similar to transmission based tomography assuming ray theoretical propagation and rayleigh scattering we pose the inverse scattering problem in tomographic form and recover perturbations in density and p and s velocities from pp and ps scattered data the method is applied to data from the southern california seismic network scsn covering the san jacinto anza region the results show a considerable correlation between seismicity and velocity perturbation structure particularly in the region between the mission creek and banning fault branches features connecting the coyote creek and elsinore faults at right angles are correlated with seismicity lineations and may represent conjugate faulting with no surface expression

probabilistic prediction of rupture length slip and seismic ground motions for an ongoing rupture implications for early warning for large earthquakes earthquake earlywarning eew predicts future ground shaking based on presently available data long ruptures present the best opportunities for eew since many heavily shaken areas are distant from the earthquake epicentre and may receive long warning times predicting the shaking from large earthquakes however requires some estimate of the likelihood of the future evolution of an ongoing rupture an eew system that anticipates future rupture using the present magnitude or rupture length together with the gutenberg richter frequencysize statistics will likely never predict a large earthquake because of the rare occurrence of extreme events however it seems reasonable to assume that large slip amplitudes increase the probability for evolving into a large earthquake to investigate the relationship between the slip and the eventual size of an ongoing rupture we simulate suites of 1 d rupture series from stochastic models of spatially heterogeneous slip we find that while large slip amplitudes increase the probability for the continuation of a rupture and the possible evolution into a big one the recognition that rupture is occurring on a spatially smooth fault has an even stronger effect we conclude that aneewsystem for large earthquakes needs some mechanism for the rapid recognition of the causative fault e g from real time gps measurements and consideration of its smoothness an eew system for large earthquakes on smooth faults such as the san andreas fault could be implemented in two ways the system could issue a warning whenever slip on the fault exceeds a few metres because the probability for a large earthquake is high and strong shaking is expected to occur in large areas around the fault a more sophisticated eew system could use the present slip on the fault to estimate the future slip evolution and final rupture dimensions and using this information could provide probabilistic predictions of seismic ground motions along the evolving rupture the decision on whether an eew system should be realized in the first or in the second way or in a combination of both is user specific

northward thinning of tibetan crust revealed by virtual seismic profiles 1 a new approach of constructing deep penetrating seismic profiles reveals significant regional variations in crustal thickness under near constant elevation of tibet over distances of hundreds of kilometers the crust is as thick as 75 km in southern tibet but shoals to just over 60 km under the qiangtang terrane in central tibet where the deviation from airy isostasy is equivalent to a thickness of over 10 km in missing crust northward thinning of crust occurs gradually over a distance of about 200 km where mechanical deformation instead of pervasive magmatism also seems to have disrupted the crust mantle interface

high resolution seismic array imaging based on an sem fk hybrid method we demonstrate the feasibility of high resolution seismic array imaging based on teleseismic recordings using full numerical wave simulations we develop a hybrid method that interfaces a frequency wavenumber fk calculation which provides analytical solutions to 1 d layered background models with a spectral element sem numerical solver to calculate synthetic responses of local media to plane wave incidence this hybrid method accurately deals with local heterogeneities and discontinuity undulations and represents an efficient tool for the forward modelling of teleseismic coda including converted and scattered waves we benchmark the accuracy of the sem fk hybrid method against fk solutions for 1 d media we then compute sensitivity kernels for teleseismic coda waves by interacting the forward teleseismic waves with an adjoint wavefield produced by injecting coda waves as adjoint sources based on adjoint techniques these sensitivity kernels provide the basis for mapping variations in subsurface discontinuities density and velocity structures through non linear conjugate gradient methods we illustrate various synthetic imaging experiments including discontinuity characterization volumetric structural inversion for the crust or subduction zones these tests show that using pre conditioners based upon the scaled product of sensitivity kernels for different phases combining finite frequency traveltime and waveform inversion and or adopting hierarchical inversions from longto short period waveforms could reduce the non linearity of the seismic inverse problem and speed up its convergence the encouraging results of these synthetic examples suggest that inversion of teleseismic coda phases based on the sem fk hybrid method and adjoint techniques is a promising tool for structural imaging beneath dense seismic arrays

evaluation of the real time earthquake information system in japan 1 the real time earthquake information system reis of the japanese seismic network is developed for automatically determining earthquake parameters within a few seconds after the p waves arrive at the closest stations using both the p wave arrival times and the timing data that p waves have not yet arrived at other stations reis results play a fundamental role in the real time information for earthquake early warning in japan we show the rapidity and accuracy of reis from the analysis of 4 050 earthquakes in three years since 2005 44 percent of the first reports are issued within 5 seconds after the first p wave arrival and 80 percent of the events have a difference in epicenter distance less than 20 km relative to manually determined locations we compared the formal catalog to the estimated magnitude from the real time analysis and found that 94 percent of the events had a magnitude difference of 1 0 unit

shdiff svdiff splitting in an isotropic earth 1 the vertically polarized svdiff seismic phase sometimes arrives later than the horizontally polarized shdiff both phases propagate in the d layer at the base of the mantle and the difference in their arrival times is usually interpreted in terms of seismic anisotropy in d using numerical simulations we demonstrate that a significant 1 s delay of svdiff relative to shdiff is present even in the iasp91 isotropic reference earth model and in a model with a high s velocity in d relative to iasp91 the delay is accompanied by strong amplitude decay of svdiff with distance this relationship resembles the effect of anelasticity in a model with a low s velocity in d the waveform of svdiff can be very different from shdiff and this difference can be mistaken for a delay of shdiff relative to svdiff in a laterally heterogeneous isotropic d svdiff can also be delayed because unlike shdiff svdiff has strong amplitude decay along fast paths its traveltime is thus dominated by slow propagation paths and tends to be positively biased for d models with an s velocity difference of 3 between two hemispheres there are regions where shdiff arrives up to 15 s earlier than the first clearly visible svdiff this is observed in a corridor several hundred kilometers wide if these effects are misinterpreted in terms of d anisotropy in actual seismic data estimates of anisotropy are biased and may contribute to the idea of seismic anisotropy being different in high and low s velocity regions of d

erodibility of cohesive streambeds in the loess area of the midwestern usa excess stress parameters critical shear stress c and erodibility coefficient k d for degrading channels in the loess areas of the midwestern usa are presented based on in situ jet testing measurements critical shear stress and k d are used to define the erosion resistance of the streambed the jet testing apparatus applies hydraulic stresses to the bed and the resulting scour due to the impinging jet is related to the excess stress parameters streams tested were primarily silt bedded in texture with low densities which is typical of loess soils results indicate that there is a wide variation in the erosion resistance of streambeds spanning six orders of magnitude for c and four orders of magnitude for k d erosion resistance was observed to vary within a streambed from streambed to streambed and from region to region an example of the diversity of materials within a river system is the yalobusha river basin in mississippi the median value of c for the two primary bed materials naheola and porters creek clay formations was 1 31 and 256 pa respectively streambeds composed of the naheola formation are readily eroded over the entire range of shear stresses whereas only the deepest flows generate boundary stresses great enough to erode streambeds composed of the porters creek clay formation therefore assessing material resistance and location is essential in classifying and modelling streambed erosion processes of these streams

first multi scale finite frequency tomography illuminates 3 d anatomy of the tibetan plateau 1 with a new multi scale parameterization 3 d images from finite frequency seismic tomography including the very first images beneath central tibet from s waves reveal that regions of low electric resistivity in the crust previously observed along active rifts in southern tibet correlate well with regions of low p and s wave speeds v however such regions are not interconnected indicating that a prevailing south directed channel like crustal flow seems inactive or this popular geodynamic model needs modification in the upper mantle there is no clear indication of regional down welling between depths of 100 to 400 km instead a strong lateral boundary between high and low v extends up to 33 n marking the northern limit of sub horizontally advancing indian lithospheric mantle

analysis of seafloor seismograms of the 2003 tokachi oki earthquake sequence for earthquake early warning 1 earthquake early warning eew algorithms estimate the magnitude of an underway rupture from the first few seconds of the p wave to allow hazard assessment and mitigation before the s wave arrival many large subduction zone earthquakes initiate 50 150 km offshore potentially allowing seafloor instruments sufficient time to identify large ruptures before the s waves reach land we tested an eew algorithm using accelerograms recorded offshore hokkaido in the region of the 2003 mw 8 1 tokachi oki earthquake and its aftershocks a wavelet transform of the first 4 s of the p wave concentrates information about earthquake magnitude from both waveform amplitude and frequency content we find that wavelets with support of a few seconds provide discriminants for eew that are both accurate enough to be useful and superior to peak acceleration or peak velocity additionally we observe a scaling of wavelet coefficient magnitude above mw 6 0 indicating that at least for the mainshock mw 8 1 and largest aftershock mw 7 1 the final size of a rupture could have been estimated from the initial portion of the seismogram

application of real time gps to earthquake early warning in subduction and strike slip environments 1 we explore the application of gps data to earthquake early warning and investigate whether the coseismic ground deformation can be used to provide fast and reliable magnitude estimations and ground shaking predictions we use an algorithm to extract the permanent static offset fromgps displacement time series and invert for theslip distribution on the fault plane which is discretized into a small number of rectangular patches we developed a completely self adapting strategy in which the initial fault plane model is built based on a quick approximate magnitude estimation and is then allowed to increase in size based on the evolutionary magnitude estimation resulting from the slip inversion two main early warning outputs are delivered in real time magnitude and the along strike extent of the rupture area these are finally used to predict the expected ground shaking due to the finite source we tested the proposed strategy by simulating real time environments for three earthquakes for themw9 0 2011 tohoku oki earthquake our algorithm provides the first magnitude estimate of 8 2 at 39 s after the origin time and then gradually increases to 8 9 at 120 s the estimated rupture length remains constant from the outset at 360 km for the mw 8 3 2003 tokachi oki earthquake the initial magnitude estimate is 8 5 at 24 s and drops to 8 2 at 40 s with a rupture length of 290 km finally for the mw 7 2 2010 el mayor cucapah earthquake the magnitude estimate is 7 0 from the outset with a rupture length of 140 km the accuracy of the ground shaking prediction using the gps based magnitude and finite extent is significantly better than existing seismology based point source approaches this approach would also facilitate more rapid tsunami warnings

time evolving seismic tomography the method and its application to the 1989 loma prieta and 2014 south napa earthquake area california we propose a time evolving approach to conduct traveltime seismic tomography in the 1989 mw 6 9 loma prieta earthquake and 2014 mw 6 0 south napa earthquake area california the recording period of the chosen seismic data between january 1 1967 and the day before the 2014 south napa earthquake is divided into two time windows separated by the 1989 loma prieta earthquake in each time window the subsurface velocity structure is iteratively updated starting from the final model of the first time window the velocity model has been successively improved throughout iterations in the second time window indicating that the traveltime data of later time windows have provided extra information to refine the subsurface images strong heterogeneities are observed in the final p wave velocity model both of the two large earthquakes occurred at transition zones in between high vp and low vp anomalies in all this study shows the effectiveness of the time evolving seismic tomography method

evolution of vertical knickpoints waterfalls with resistant caprock insights from numerical modeling 1 vertical knickpoints waterfalls mark a prominent process transition zone whose governing mechanics is not represented by conventional stream power incision models we examine the evolution of vertical knickpoints with resistant caprock utilizing numerical simulations that explicitly represent 1 face failure mechanisms 2 flow acceleration and amplified erosion above a knickpoint lip 3 deposition and removal of coarse debris below the knickpoint and 4 base level lowering or tectonic uplift rates our model demonstrates that knickpoint retreat rate where the subcaprock is weak or vertically jointed and base level fall rates are steady is likely to become tied to downstream conditions and equal to the downstream incision rate divided by channel gradient mechanically this coupling occurs where the subcaprock reaches a threshold height for failure in shear or buckling or where the weathering rate of the subcaprock is higher than the downstream incision wave velocity vi ds the height of the subcaprock face can influence its gravitational stability and the knickpoint lateral erosion rate and lead to a feedback between downstream incision and retreat rate retreat rate can be lower than vi ds during transients which could be long 106 years and set by the weathering rate of the subcaprock or influenced by lag debris evacuation key variables other than discharge can be important in setting retreat rates these include base level lowering rate the rock strength of stratigraphic units downstream of the knickpoint and the size and flux of sediment contributed from above the knickpoint or from the canyon walls two types of oversteepened reaches can form in association with a vertical knickpoint 1 an upstream free fall induced oversteepened reach whose length is longer than the flow acceleration zone and 2 a downstream coarse debris induced oversteepened reach although the model was constructed with caprock type knickpoints in mind some of its elements and insights are also relevant to homogenous substrates

early magnitude and potential damage zone estimates for the great mw 9 tohoku oki earthquake the mw 9 0 2011 tohoku oki earthquake has reopened the discussion among the scientific community about the effectiveness of earthquake early warning for large events a well known problem with real time procedures is the parameter saturation which may lead to magnitude underestimation for large earthquakes here we measure the initial peak ground displacement and the predominant period by progressively expanding the time window and distance range to provide consistent magnitude estimates m 8 4 and a rapid prediction of the potential damage area this information would have been available 35 s after the first p wave detection and could have been refined in the successive 20 s using data from more distant stations we show the suitability of the existing regression relationships between early warning parameters and magnitude provided that an appropriate p wave time window is used for parameter estimation we interpret the magnitude under estimation as a combined effect of high pass filtering and frequency dependence of the main radiating source during the rupture process

a hybrid method to compute short period synthetic seismograms of teleseismic body waves in a 3 d regional model we present a hybrid method to simulate the propagation of short period teleseismic body waves through 3 d regional models the incident wavefield is computed in an spherically symmetric reference earth model based on the direct solution method the global and regional wavefields are matched at the boundaries of the regional mesh in the regional domain we implement a spectral element method with absorbing boundaries to cancel the outgoing scattered wavefield the hybrid method is successfully benchmarked against the direct solution method in the reference earth model iasp91 the potential of the method is illustrated by computing short period p wave synthetic seismograms in a 3 d model with a 20 km moho offset and or topography on the free surface focusing on the actual example of the pyrenees

examination of scaling between earthquake magnitude and proposed early signals in p waveforms from very near source stations in a south african gold mine 1 we analyze near source seismograms recorded in a deep south african mine for scaling between signals early in p waveforms and the magnitude m of the events the data consist of recordings at 26 stations of 122 events with 1 5 0 implying that the final earthquake size is affected statistically by the initial rupture process if these correlations hold for larger earthquakes as suggested by other studies the early predominant period and peak displacement are useful for early warning systems

seismic receiver functions and the lithosphere asthenosphere boundary abstract the lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists since it is relatively poorly observed by seismic means there is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves seismic techniques which use shorter period p to s or s to p converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution the principle of this technique the so called receiver function technique is that a strong teleseismic mother phase e g p s pp or sks incident from below on any seismic discontinuity beneath a station produces a converted phase ps or sp which indicates its depth and properties we discuss details of this technique a sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought an intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves this confirms earlier results from controlled source observations thybo and perchuc 1997 we discuss possible interpretations of this shallow low velocity zone in cratonic regions

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

rapid estimation of earthquake source and ground motion parameters for earthquake early warning using data from a single three component broadband or strong motion sensor we propose a new algorithm to rapidly determine earthquake source and ground motion parameters for earthquake early warning eew this algorithm uses the acceleration velocity and displacement waveforms of a single three component broadband bb or strong motion sm sensor to perform real time earthquake noise discrimination and near far source classification when an earthquake is detected the algorithm estimates the moment magnitude m epicentral distance and peak ground velocity pgv at the site of observation the algorithm was constructed by using an artificial neural network ann approach our training and test datasets consist of 2431 three component sm and bb records of 161 crustal earthquakes in california japan and taiwan with 3 1 m 7 6 at 115 km first estimates become available at t 0 0 25 s after the p pick and are regularly updated we find that displacement and velocity waveforms are most relevant for the estimation of m and pgv while acceleration is important for earthquake noise discrimination including site corrections reduces the errors up to 10 the estimates improve by an additional 10 if we use both the vertical and horizontal components of recorded ground motions the uncertainties of the predicted parameters decrease with increasing time window length t 0 larger magnitude events show a slower decay of these uncertainties than small earthquakes we compare our approach with the c algorithm and find that our prediction errors are around 60 smaller however in general there is a limitation to the prediction accuracy an eew system can provide if based on single sensor observations

earthquake magnitude estimation from early radiated energy 1 from inspection of a large set of japanese events we investigate the scaling of the early radiated energy inferred from the squared velocity integral iv2 with the final magnitude of the event we found that the energy can only discriminate whether the event has a magnitude larger or smaller than 5 8 and in the latter case it can allow for real time magnitude estimation however by normalizing iv2 for the rupture area the initial slip scales with the magnitude between 4 m 7 following the expected scaling laws we show that the ratio between the squared peak displacement and iv2 is a proxy for the slip following the same scaling but it can be directly derived from the data without any assumption on the rupture area the scaling relationship between initial slip and magnitude can be used for early warning applications when integrated in a probabilistic evolutionary approach

earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records 1 we show that the low pass filtered peak amplitudes of initial p and s wave seismic signals recorded in the vicinity of an occurring earthquake source correlates with the earthquake magnitude and may be used for real time estimation of the event size in seismic early warning applications the earthquake size can be therefore estimated using only a couple of seconds of signal from the p or s wave onsets i e while the rupture itself is still propagating and rupture dimension is far from complete we argue that dynamic stress release and or slip duration on the fault in the very early stage of seismic fracture scales both with the observed peak amplitude and with the elastic energy available for fracture propagation the probability that a fracture grows to a larger size should scale with the energy initially available citation zollo a m lancieri and s nielsen 2006 earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records geophys res lett 33 l23312 doi 10 1029 2006gl027795