litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

identifying space time clustering properties of the 1983 1997 irpinia basilicata southern italy seismicity abstract the fractality of the earthquake sequence 1983 1997 of irpinia basilicata southern italy one of the most seismically active regions of the mediterranean area has been analysed by temporal and spatial fractal tools the fractal exponent estimated by the allan factor method characterises the time clustering behaviour of the set of earthquakes while the correlation dimension d c calculated by means of the correlation integral method gives information on the space clustering behaviour of the sequence of seismic events analysing the variations of both the parameters we recognised the presence of a strong space time clusterisation associated with the major events that occurred in the investigated area

on crustal corrections in surface wave tomography summary mantle models from surface waves rely on good crustal corrections we investigated how far ray theoretical and finite frequency approximations can predict crustal corrections for fundamental mode surface waves using a spectral element method we calculated synthetic seismograms in transversely isotropic prem and in the 3 d crustal model crust2 0 on top of prem and measured the corresponding time shifts as a function of period we then applied phase corrections to the prem seismograms using ray theory and finite frequency theory with exact local phase velocity perturbations from crust2 0 and looked at the residual time shifts after crustal corrections residuals fall within the uncertainty of measured phase velocities for periods longer than 60 and 80 s for rayleigh and love waves respectively rayleigh and love waves are affected in a highly non linear way by the crustal type oceanic crust affects love waves stronger while rayleigh waves change most in continental crust as a consequence we find that the imperfect crustal corrections could have a large impact on our inferences of radial anisotropy if we want to map anisotropy correctly we should invert simultaneously for mantle and crust the latter can only be achieved by using perturbation theory from a good 3 d starting model or implementing full non linearity from a 1 d starting model

systematic survey of high resolution b value imaging along californian faults inference on asperities understanding and forecasting earthquake occurrences is presumably linked to understanding the stress distribution in the earth s crust this cannot be measured instrumentally with useful coverage however the size distribution of earthquakes quantified by the gutenberg richter b value is possibly a proxy to differential stress conditions and could therewith act as a crude stress meter wherever seismicity is observed in this study we improve the methodology of b value imaging for application to a high resolution 3 d analysis of a complex fault network in particular we develop a distance dependent sampling algorithm and introduce a linearity measure to restrict our output to those regions where the magnitude distribution strictly follows a power law we assess the catalog completeness along the fault traces using the bayesian magnitude of completeness method and systematically image b values for 243 major fault segments in california we identify and report b value structures revisiting previously published features e g the parkfield asperity and documenting additional anomalies e g along the san andreas and northridge faults combining local b values with local earthquake productivity rates we derive probability maps for the annual potential of one or more m6 events as indicated by the microseismicity of the last three decades we present a physical concept of how different stressing conditions along a fault surface may lead to b value variation and explain nonlinear frequency magnitude distributions detailed spatial b value information and its physical interpretation can advance our understanding of earthquake occurrence and ideally lead to improved forecasting ability

earthquakes recurrence and interoccurrence times the purpose of this paper is to discuss the statistical distributions of recurrence times of earthquakes recurrence times are the time intervals between successive earthquakes at a specified location on a specified fault although a number of statistical distributions have been proposed for recurrence times we argue in favor of the weibull distribution the weibull distribution is the only distribution that has a scale invariant hazard function we consider three sets of characteristic earthquakes on the san andreas fault 1 the parkfield earthquakes 2 the sequence of earthquakes identified by paleoseismic studies at the wrightwood site and 3 an example of a sequence of micro repeating earthquakes at a site near san juan bautista in each case we make a comparison with the applicable weibull distribution the number of earthquakes in each of these sequences is too small to make definitive conclusions to overcome this difficulty we consider a sequence of earthquakes obtained from a one million year virtual california simulation of san andreas earthquakes very good agreement with a weibull distribution is found we also obtain recurrence statistics for two other model studies the first is a modified forest fire model and the second is a slider block model in both cases good agreements with weibull distributions are obtained our conclusion is that the weibull distribution is the preferred distribution for estimating the risk of future earthquakes on the san andreas fault and elsewhere

investigating non uniform scaling behavior in ultra low frequency ulf earthquake related geomagnetic signals abstract the scaling properties of the time dynamics of 2000 2001 ulf geomagnetic data in the frequency range between 1 mhz and 10 hz observed at izu peninsula in japan were investigated on the basis of detrended fluctuation analysis dfa which is a powerful method to detect scaling in non stationary time series deviations from uniform power law scaling were identified and quantified our results suggest that a significant non uniform scaling behavior in ulf geomagnetic data could be related to the occurrence of intense seismic clusters these first results could be useful in the framework of short term earthquake prediction

a bayesian approach to assess the importance of crustal corrections in global anisotropic surface wave tomography several recent studies have demonstrated the importance of crustal corrections when inverting surface wave data to model lateral variations in mantle radial anisotropy it has also been shown that the choice of the prior crustal model to correct the data can strongly influence the anisotropy model and potentially lead to different geodynamic interpretations in comparing tomographic models of radial anisotropy obtained from different crustal corrections these studies did not however determine quantitative model uncertainties nevertheless mantle models resulting from different prior crustal corrections are statistically different only if the posterior model errors stemming from the non uniqueness of the inverse problem are smaller than the effect of the crustal correction itself here we applied a model space search approach to global fundamental and higher mode rayleigh and love wave phase velocity maps to determine reliable quantitative model uncertainties on seismic velocities and radial anisotropy the technique employed enabled us to describe the model space with a posterior probability density function and therefore to test whether models obtained from different crustal corrections are statistically different we thus assessed the significance of the choice of the crustal model by comparing the posterior model errors to the differences in mantle structure resulting from different crustal corrections we tested prior crustal models crust2 0 crust1 0 and 3smac our study shows that the use of prior crustal corrections from different crustal models yields significant discrepancies in mantle velocities around 50 km depth and in radial anisotropy down to 100 km the impact of the crustal correction on radial anisotropy can extend down to 250 km in some locations we found that choosing 3smac instead of the other crustal models has a stronger influence on the mantle model but that crust1 0 and crust2 0 yield statistically identical anisotropy models at all depths except at a few grid cells importantly the effect of the crustal model is most significant in continental regions and not so much beneath oceans which has important consequences for determining the depth of continental roots our results therefore suggest that improving constraints on crustal structure in continents is essential for our understanding of continent formation our work also demonstrates that the prior crustal model does not significantly affect radial anisotropy and velocities at depths greater than 100 km this implies that if geodynamic interpretations of radial anisotropy below 100 km depth were to account for tomographic model uncertainties they would not depend on the choice of the prior crustal model it is therefore important for geodynamicists and seismologists to work in concert and to put effort into determining quantitative tomographic model uncertainties before interpreting the results our results also caution against the use of 3smac to correct surface wave data for studies of the continental lithosphere and suggest that the solid earth community would benefit from putting some efforts toward building a revised 3smac the discrepancies between mantle models built based on 3smac crustal corrections and those based on crust1 0 or crust2 0 should also help shed light on the validity of the geodynamical assumptions made in the construction of models like 3smac

multiparametric statistical investigation of seismicity occurred at el hierro canary islands from 2011 to 2014 abstract a detailed statistical investigation of the seismicity occurred at el hierro volcano canary islands from 2011 to 2014 has been performed by analysing the time variation of four parameters the gutenberg richter b value the local coefficient of variation the scaling exponent of the magnitude distribution and the main periodicity of the earthquake sequence calculated by using the schuster s test these four parameters are good descriptors of the time and magnitude distributions of the seismic sequence and their variation indicate dynamical changes in the volcanic system these variations can be attributed to the causes and types of seismicity thus allowing to distinguish between different host rock fracturing processes caused by intrusions of magma at different depths and overpressures the statistical patterns observed among the studied unrest episodes and between them and the eruptive episode of 2011 2012 indicate that the response of the host rock to the deformation imposed by magma intrusion did not differ significantly from one episode to the other thus suggesting that no significant local stress changes induced by magma intrusion occurred when comparing between all them therefore despite the studied unrest episodes were caused by intrusions of magma at different depths and locations below el hierro island the mechanical response of the lithosphere was similar in all cases this suggests that the reason why the first unrest culminated in an eruption while the other did not may be related to the role of the regional local tectonics acting at that moment rather than to the forceful of magma intrusion

the weibull log weibull transition of interoccurrence time for synthetic and natural earthquakes abstract we study the interoccurrence time distributions of events by analyzing synthetic catalogues and three natural catalogues of the japan meteorological agency jma the southern california earthquake data center scedc and the taiwan central weather bureau tcwb we find a universal feature i e the weibull log weibull transition in the interoccurrence time statistics this transition demonstrates that the interoccurrence time statistics of earthquakes possess the hybrid weibull and log weibull statistics we further find that the crossover magnitude m c from the superposition regime to the pure weibull regime is averagely proportional to the plate velocity in the end of this paper we summarize a region independent relation i e m c m max 0 54 0 06 which represents a novel empirical relation related to the weibull log weibull transition for earthquake processes

crustal structure of the caribbean northeastern south america arc continent collision zone 1 we present the results of a 568 km long regional wide angle seismic profile conducted in the southeastern caribbean that crosses an active island arc a remnant arc two basins possibly floored by oceanic crust an allochthonous terrane of forearc affinity and the passive margin of northern south america the velocity structures of the late cretaceous aves ridge remnant arc and miocene and younger lesser antilles arc are remarkably similar which implies that magmatic processes have remained moderately steady over time crustal thickness is 26 km at the aves ridge and 24 km at the lesser antilles arc in comparison to the izu bonin and aleutian arcs the lesser antilles arc is thinner and has no evidence for a lower crustal cumulate layer which is consistent with the estimated low magma production rates of the lesser antilles arc crustal thickness beneath the grenada and tobago basins is 4 10 km and the velocity structure suggests that these basins could be floored by oceanic crust a decrease of 1 km s in average seismic velocity of the upper crust is observed from nw to se across the north coast fault zone we argue that this marks the suture between the far traveled caribbean arc and the passive margin of the south american continent current strike slip motion between the caribbean and south american plates is located 30 km to the south and thus material originally deposited on the south american passive margin has now been transferred to the caribbean plate

waveform tomography reveals channeled flow at the base of the oceanic asthenosphere understanding the relationship between different scales of convection that drive plate motions and hotspot volcanism still eludes geophysicists using full waveform seismic tomography we imaged a pattern of horizontally elongated bands of low shear velocity most prominent between 200 and 350 kilometers depth which extends below the well developed low velocity zone these quasi periodic fingerlike structures of wavelength 2000 kilometers align parallel to the direction of absolute plate motion for thousands of kilometers below 400 kilometers depth velocity structure is organized into fewer undulating but vertically coherent low velocity plumelike features which appear rooted in the lower mantle this suggests the presence of a dynamic interplay between plate driven flow in the low velocity zone and active influx of low rigidity material from deep mantle sources deflected horizontally beneath the moving top boundary layer

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

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

generic dependence of the frequency size distribution of earthquakes on depth and its relation to the strength profile of the crust 1 we explore the idea that the relative size distribution of earthquakes quantified using the so called b value is negatively correlated with differential stress because the maximum possible differential stress increases linearly in the brittle upper crust we expect to find a decrease of b with depth we test this expectation for seven continental areas around the world each of which is described by a regional earthquake catalog we find a monotonic decrease in b value between 5 and 15 km depth the decrease stops near the brittle ductile transition we specifically focus on the high quality catalogs of earthquakes in california to perform a sensitivity test with respect to depth uncertainty we also estimate the probability depth gradient for the occurrence of a target magnitude event and study the behavior of b with depth in near and off fault zones we also translate the observed b depth gradients into b differential stress gradients our findings suggest that b values are negatively correlated with differential stress and hus have the potential to act as stress meters in the earth s crust

inferring upper mantle structure by full waveform tomography with the spectral element method summary mapping the elastic and anelastic structure of the earth s mantle is crucial for understanding the temperature composition and dynamics of our planet in the past quarter century global tomography based on ray theory and first order perturbation methods has imaged long wavelength elastic velocity heterogeneities of the earth s mantle however the approximate techniques upon which global tomographers have traditionally relied become inadequate when dealing with crustal structure as well as short wavelength or large amplitude mantle heterogeneity the spectral element method on the other hand permits accurate calculation of wave propagation through highly heterogeneous structures and is computationally economical when coupled with a normal mode solution and applied to a restricted region of the earth such as the upper mantle sem importantly sem allows a dramatic improvement in accounting for the effects of crustal structure here we develop and apply a new hybrid method of tomography which allows us to leverage the accuracy of sem to model fundamental and higher mode long period 60 s waveforms we then present the first global model of upper mantle velocity and radial anisotropy developed using sem our model semum confirms that the long wavelength mantle structure imaged using approximate semi analytic techniques is robust and representative of the earth s true structure furthermore it reveals structures in the upper mantle that were not clearly seen in previous global tomographic models we show that semum favourably compares to and rivals the resolving power of continental scale studies this new hybrid approach to tomography can be applied to a larger and higher frequency data set in order to gain new insights into the structure of the lower mantle and more robustly map seismic structure at the regional and smaller scales

a detailed subduction structure in the kuril trench deduced from ocean bottom seismographic refraction studies abstract in 1983 we conducted an ocean bottom seismograph obs experiment in the southernmost part of the kuril trench beneath which the pacific plate is subducting under hokkaido island japan the aim of this experiment was to determine crust and upper mantle structure from the oceanic basin to the continental slope by dense seismic refraction profiling using explosives and airguns the total length of the profiles was 560 km along which ten obs s were deployed the observed data were of good quality which enabled us to obtain a detailed velocity structure of the active margin down to 20 30 km we constructed a velocity structure model by ray tracing and amplitude modeling in the oceanic basin the crust has a typical oceanic structure characterized by three layers with p wave velocities of 1 8 3 8 6 5 and 6 5 7 0 km s the velocity gradient in layer 3 increases downward from 0 075 to 0 10 s 1 the moho discontinuity was well constrained by clearly observed p n and p m p phases the total thickness of the oceanic crust was determined to be 8 km and almost constant in the oceanic basin the p wave velocity is 7 9 km s beneath the moho discontinuity which increases downward with a rather small velocity gradient 0 015 0 03 s 1 beneath the continental slope we found relatively low velocity 2 5 to 5 5 5 8 km s material the oceanic moho discontinuity associated with the subducting plate was traced down to a depth of 25 km our seismic data strongly suggest that oceanic layer 2 is smoothly subducting and does not break up to form a wedge structure this result is in remarkable contrast with the velocity structure in the active margin of the ryukyu trench area about 1000 km south of the present experimental area where we found a 12 km thick prominent low velocity wedge is situated 50 150 km landward from the trench axis on the seaward side of the wedge the surface of the igneous basement undulates severely the wedge was probably formed by materials of oceanic origin such a difference in velocity structure suggests that the subduction mechanism in the trench area differs from region to region in the northwestern pacific

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

deep crustal structure in the eastern gulf of mexico we use air gun data recorded by ocean bottom seismometers to constrain the velocity structure along gulf of mexico basin opening line 4 a profile extending from the northwestern florida peninsula across the florida escarpment to the central gulf of mexico moderately thinned continental crust with a moho depth of 32 33 km average sediment thickness of 6 km and an average crustal thickness of 27 km is interpreted on the northeast end of the profile offshore florida thinned and intruded continental crust is identified over a horizontal distance of 225 km where the crustal layer thins from 25 km to 6 7 km mean seismic velocities of the crust in this region increase from 6 55 km s to 6 95 km s from northeast to southwest and are evidence for increased magmatic input as rifting developed oceanic crust with an average thickness of 5 6 5 7 km is observed over a distance of 175 km on the southwest end of the profile with an extinct spreading ridge with an axial valley morphology imaged on a coincident seismic reflection profile anomalously high upper oceanic crust velocities of 6 0 6 7 km s are interpreted as massive basalt flows and could reflect increased temperatures during emplacement integrating well seismic reflection and our seismic refraction data allow us to estimate a full spreading rate of 2 2 cm yr for seafloor spreading along the profile this indicates that oceanic crust was emplaced at a slow spreading center

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

the taiwan telemetered seismographic network abstract in 1972 the taiwan telemetered seismographic network ttsn was installed to monitor earthquakes occurring in an area from 21 to 26 n latitude and from 119 to 123 e longitude the number of stations increased from six in 1972 to 24 in 1987 the stations are equipped with velocity type seismometers with a natural frequency of 1 hz since 1983 horizontal component sensors have been added at several stations signals recorded by the field stations are transmitted to taipei recording center through telephone lines or radio and then recorded on fm magnetic tapes paper and nine track magnetic tapes through a d converters hypocenters of earthquakes are routinely determined by a hypoc2 computer program the size of an earthquake is estimated from the signal duration moreover a simulated wood anderson seismographic station is in operation at taipei for the determination of local magnitude a seismic work system sws is being established for automatic data acquisition and data processing to avoid clipping of signal amplitude an optimum telemetry system is being linked to the ttsn

non linear crustal corrections in high resolution regional waveform seismic tomography summary we compare 3 d upper mantle anisotropic structures beneath the north american continent obtained using standard and improved crustal corrections in the framework of non linear asymptotic coupling theory nact applied to long period three component fundamental and higher mode surface waveform data our improved approach to correct for crustal structure in high resolution regional waveform tomographic models goes beyond the linear perturbation approximation and is therefore more accurate in accounting for large variations in moho topography within short distances as observed for instance at ocean continent margins this improved methodology decomposes the shallow layer correction into a linear and non linear part and makes use of 1 d sensitivity kernels defined according to local tectonic structure both for the forward computation and for the computation of sensitivity kernels for inversion the comparison of the 3 d upper mantle anisotropic structures derived using the standard and improved crustal correction approaches shows that the model norm is not strongly affected however significant variations are observed in the retrieved 3 d perturbations the largest differences in the velocity models are present below 250 km depth and not in the uppermost mantle as would be expected we suggest that inaccurate crustal corrections preferentially map into the least constrained part of the model and therefore accurate corrections for shallow layer structure are essential to improve our knowledge of parts of the upper mantle where our data have the smallest sensitivity

improving global radial anisotropy tomography the importance of simultaneously inverting for crustal and mantle structure observed seismic anisotropy gives the most direct information on mantle flow but it is challenging to image it robustly at global scales difficulties in separating crustal from mantle structures in particular can have a strong influence on the imaging here we carry out several resolution tests using both real and synthetic data which show that unconstrained crustal structure can strongly contaminate retrieved radial anisotropy at 100 150 km depth to efficiently reduce crustal effects we perform whole mantle radially anisotropic tomographic inversions including crustal thickness perturbations as model parameters our data set includes short period group velocity data which are sensitive to shallow structure we perform a series of tests that highlight the advantages of our approach and show that to properly constrain thin oceanic crust in global radially anisotropic inversions group velocity data with wave periods of at least t 20 s or shorter are required our moho perturbation model shows thicker crust along subduction zones and beneath the ontong java plateau in the southwestern pacific than in the global crustal model crust2 0 these features agree well with other crustal models as well as with refraction survey data and tectonic features in these regions

structural variations of arc crusts and rifted margins in the southern izu ogasawara arc back arc system 1 we carried out a reflection refraction seismic survey across the southern izu ogasawara arc back arc system covering three arcs with different crustal ages the oldest eocene arc has middle and lower crust with high velocities of 6 4 6 6 and 6 8 7 4 km s respectively suggesting denser crustal materials the current volcanic arc has middle and lower crust with lower velocities of 5 7 6 5 and 6 7 7 1 km s suggesting advanced crustal differentiation the crust mantle transition layer with a velocity of 7 5 8 0 km s is distributed beneath the current volcanic arc and the rear arc suggesting a pool of dense materials emanating from the crust through the crustal growth these structural differences between the eocene arc and current arc indicate a difference of crustal growth based on basaltic and andesitic magmas according to known petrologic studies commonly rifted crusts have lower crusts with high velocities of over 7 0 km s and the arc back arc transition zone also has a thinner more reflective crust that may have been affected by postrifting magmatism

receiver function study of the crustal structure of the southeastern caribbean plate boundary and venezuela 1 we have investigated crustal thickness and composition across the southeastern caribbean plate boundary with the receiver function technique we used teleseismic data recorded by a temporary broadband array deployed under the bolivar project and the permanent national seismic network of venezuela we used the primary p to s conversion and crustal reverberations to estimate crustal thickness and average crustal vp vs ratio over the region we observe large variations in crustal thickness and poisson s ratio estimated moho depth ranges from 16 km beneath the southeastern caribbean sea to 52 km beneath northeastern venezuela and the venezuelan andes there is a good correlation between crustal structure and tectonic terranes data from the precambrian guayana shield suggest that the underlying crustal structure is relatively uniform with a moderate thickness 37 km and an intermediate composition a thick crust is found below the foreland basins the two mountain systems in northern venezuela the serrania del interior and the serrania del falcon have a thin crust with arc composition and are likely dynamically supported by elastic rebound or underthrusting of the oceanic plateau that characterizes the southern caribbean on the other hand the venezuelan andes and perija range on the western side of the country are probably isostatically balanced by thick crustal roots

statistical evaluation of characteristic earthquakes in the frequency magnitude distributions of sumatra and other subduction zone regions 1 if subduction zone earthquakes conform to a characteristic model in which persistent segments fail at predictable stress levels due to the steady accumulation of tectonic loading historical seismicity may constrain the occurrence of future events we test this model for earthquakes on the sumatra andaman megathrust and other subduction zones using frequency magnitude distributions using simulations we show that poisson confidence intervals correctly account for the counting errors of histogram data these confidence intervals demonstrate that we cannot reject the gutenberg richter distribution in favor of a characteristic model in any of the real catalogues tested a visual bias in power law count data at high magnitudes combined with a sample bias for large earthquakes is sufficient to explain candidate characteristic events this result implies that historical earthquakes are likely poor models for future events and that monte carlo simulations will provide a better assessment of earthquake and associated hazards

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

deep structure and seismic anisotropy beneath the east pacific rise seismic velocities in the upper mantle beneath mid ocean ridges are known to exhibit anisotropy especially at depths shallower than 200 km in this study we present evidence for deeper anisotropy beneath fast spreading ridges based on simultaneous inversion of body wave travel times waveforms and surface wave phase velocities the dverticalt bsv shear wave speed is systematically faster by more than 2 than the dhorizontalt bsh one at depths of 200 300 km beneath the east pacific rise a result that is consistent with vertical alignment of the fast crystallographic axis of olivine this anomaly is especially coherent beneath the northern east pacific rise where the observations also support the presence of a modest mantle reflector near 260 km depth the anisotropy may be associated with deep vertical flow or finite strain and the presence of this reflector could signal a rheological transition near the bottom of the asthenosphere reflecting changes in flow direction development of partial melt or the persistence of a deep pre existing strain regime d 2005 elsevier b v all rights reserved

joint inversion for global isotropic and radially anisotropic mantle structure including crustal thickness perturbations we present a new global whole mantle model of isotropic and radially anisotropic s velocity structure sglobe rani based on 43 000 000 surface wave and 420 000 body wave travel time measurements which is expanded in spherical harmonic basis functions up to degree 35 we incorporate crustal thickness perturbations as model parameters in the inversions to properly consider crustal effects and suppress the leakage of crustal structure into mantle structure this is possible since we utilize short period group velocity data with a period range down to 16 s which are strongly sensitive to the crust the isotropic s velocity model shares common features with previous global s velocity models and shows excellent consistency with several high resolution upper mantle models our anisotropic model also agrees well with previous regional studies anomalous features in our anisotropic model are faster sv velocity anomalies along subduction zones at transition zone depths and faster sh velocity beneath slabs in the lower mantle the derived crustal thickness perturbations also bring potentially important information about the crustal thickness beneath oceanic crusts which has been difficult to constrain due to poor access compared with continental crusts

analysis of time dynamical features in intraplate versus interplate seismicity the case study of iquique area chile the intraplate and interplate seismic catalogues of iquique chile area were investigated by using seismological b value of the gutenberg richter law fractal allan factor and detrended fluctuation analysis and topological horizontal visibility graph methods the two catalogues show different stress state indicated by the different b value larger for the intraplate seismicity the interplate seismicity shows significant time clustering behavior of the earthquake occurrence times at large time scales while the time distribution of the intraplate earthquakes seems to be featured by random fluctuations without any significant sign of time clustering different role seems to be played by aftershocks in the two investigated seismic zones revealed by the different time distribution of the aftershock depleted catalogue of the intraplate zone which remains poissonian for most of the time scales and the interplate zone that still keeps its clustering phenomenon but at higher timescales thus shortening its clustering time scale range furthermore the interevent times of the interplate catalogue are characterized by persistent dynamics even after removing the aftershocks while uncorrelated fluctuations characterize the behavior of interevent intervals of the whole as well as aftershock depleted intraplate catalogue additionally the magnitudes of both catalogues are characterized by time reversibility before and after the aftershock removal while the interevent times of intraplate catalogue change their status from time irreversibility to time reversibility after removing the aftershocks the obtained results seem to evidence a different role played by the aftershocks in the intraplate and interplate zones that needs to be further explored

characterizing the caribbean south american plate boundary at 64 w using wide angle seismic data 1 we present wide angle velocity modeling results from profile 64 w of the broadband ocean land investigation of venezuela and the antilles arc region bolivar project line 64w is a 460 km long approximately north south onshore offshore reflection refraction transect located approximately at 64 w longitude the profile extends across the transform plate boundary between the southeastern caribbean car and south american sa plates east of the profile the plate boundary bends to the north and sa subducts beneath car we utilize first arrival tomography to resolve a smooth velocity field for the sediments and upper middle crust and then use a layered approach to resolve a sharp velocity contrast for the moho simultaneously inverting refracted pn and reflected pmp arrivals we image crustal and upper mantle structure across the plate boundary zone we interpret that the strike slip system that accommodates relative motion between car and sa extends near vertically through the entire crust and offsets the moho we see no evidence supporting a major component of convergence and rather than a wide boundary zone of overlapping lithospheric plates we interpret the plate boundary to be confined to the 33 km wide near vertical strike slip system previously interpreted thrust faults flanking the strike slip system appear to be confined to the upper middle crust and may be related to the detachment of subducting south american lithosphere at the southern terminus of the lesser antilles subduction zone east of 64 w

structural factors controlling the rupture process of a megathrust earthquake at the nankai trough seismogenic zone summary the nankai trough is a vigorous subduction zone where large earthquakes have been recorded with a recurrence time of 100 200 yr the 1946 nankaido earthquake is well known as an unusual event among these earthquakes because the rupture zone estimated from long period geodetic data is more than twice as large as that derived from seismic wave data in the summer of 1999 an onshore offshore deep seismic survey was performed along a 355 km long profile in the western nankai trough seismogenic zone seismic signals both from an airgun array 207 l and land explosions maximum of 500 kg were recorded simultaneously by 98 oceanbottom seismographs and 93 land seismic stations conventional 2 d seismic reflection data were also acquired along part of the offshore profile from the wide angle seismic data we found a subducting seamount at the centre of the proposed rupture zone with dimensions of 13 km thick by 50 km wide at 10 km depth the seismic velocity image also shows that the seamount is now colliding with the japanese island arc crust from this significant structure this paper proposes that the subducted seamount functioned as a barrier at least during the 1946 earthquake i e the rupture of the 1946 earthquake extended over the entire locked zone to the east of the subducted seamount and then the rupture was deflected around the subducted seamount at the down dip end of the locked zone between cape muroto and cape ashizuri another significant structure a highly reflective layer is obtained beneath shikoku island a very slow p wave velocity 3 km s 1 is necessary in a thin layer at the base of the island arc crust in order to explain the observed high amplitude reflection phases an area of low resistivity obtained by a previous magnetotelluric study corresponds to the highly reflective layer this suggests a possible water layer at the base of the island arc crust the water may be generated by dehydration of the downgoing probably partially serpentinized mantle which is implied by a low p wave velocity 7 5 km s 1 beneath the subducted seamount a locally observed non slip region during the 1946 earthquake at the eastern part of shikoku island is interpreted as a result of weak coupling at the possible water layer

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

fractal and spectral investigation of the shallow seismicity in taiwan abstract we studied the whole and aftershock depleted shallow depth 30 km taiwanese seismicity from 1990 to 2017 by using several independent methods the coefficient of variations and the allan factor have revealed that time clustering characterizes not only the time distribution of the whole seismic catalogue but also that of the aftershock depleted one although this displays time clustering at larger timescales in particular the allan factor shows that at small timescales the seismic process of the whole as well as the aftershock depleted one can be well described by a poisson process the detrended fluctuation analysis clearly evidence persistence in the interevent times and weak persistence or randomness in the magnitudes the singular spectrum analysis of the daily counts in the aftershock depleted catalogue reveals the existence of quasi monthly and bi weekly periodicities furthermore quasi annual and quasi semestral periodicities have been identified that strengthen the link between seismic activity in taiwan and earth s tides

non uniform scaling features in central italy seismicity a non linear approach in investigating seismic patterns and detection of possible earthquake precursors 1 the detrended fluctuation analysis dfa is a powerful method for capturing scaling behavior in nonstationary time series using an appropriate instability index it is possible to identify and quantify deviations from uniform power law scaling which suggest the presence of changing dynamics in the system under study in this context the scaling behavior of the 1981 2007 seismicity in umbria marche central italy which is one of the most seismically active areas in italy was investigated significant deviations from uniform power law scaling in the seismic temporal fluctuations were revealed mostly linked with the occurrence of rather large earthquakes or seismic clusters

crustal and upper mantle structure in the ryukyu island arc deduced from deep seismic sounding summary in 1984 an extensive geophysical investigation was conducted in the northernmost part of the ryukyu island arc south of kyushu island japan the aim of this investigation was to obtain new information on the nature of crust and upper mantle at the continental margin through various geophysical measurements seismic profiling gravity magnetism sea beam and heat flow this paper presents the crust and upper mantle structure deduced from ocean bottom seismographic profiling conducted along two lines one line 190 km long was taken behind the northernmost part of the ryukyu island arc parallel to the major tectonic units i e the okinawa trough ryukyu arc and ryukyu trench the other 295 km long was perpendicular to the tectonic units along these profiles we deployed ocean bottom seismograms spaced 10 20km apart as a controlled source we used both explosives and an airgun array the experiment was successful and provided quite important information on the tectonics of a trenchisland arc back arc system the velocity structure obtained for the profile behind the ryukyu islands has continental properties the sediment thickness is 3 4 km although it shows lateral variations due to basement undulation the velocities of the upper and lower crust are 5 8 6 2 and 6 6 6 8 km s respectively the total crustal thickness decreases southwestward from 27 30 to 23 24 km this is direct evidence for crustal thinning associated with the process of back arc spreading the velocity structure along the profile from the trench to the island arc clearly shows the subduction accretion and deformation at this margin the crust beneath the trench has oceanic properties the sediment thickness is 1 3 3 0 km beneath which the igneous basement shows severe undulation the total crustal thickness is 7 8 km the p velocity is slightly less than 8 0 km s our seismic data revealed a huge sedimentary wedge located 50 150 km landward of the trench the maximum thickness of this wedge exceeds 12 km the origin of this wedge may be oceanic because the p wave velocity in its eastern half is almost comparable to that obtained for the trench area the velocity structure landward of the wedge is continental and similar to that obtained for the profile behind the island arc

global radially anisotropic mantle structure from multiple datasets a review current challenges and outlook abstract since the 1960s seismologists have mapped anisotropy in the uppermost mantle the mantle transition zone and the d region when combined with constraints from mineral physics and geodynamics anisotropy provides critical information on the geometry of mantle flow here we review the theory early work recent tomographic models and experimental constraints on radial anisotropy we discuss current challenges in resolving radial anisotropy seismically in particular we show that it is highly beneficial to use multiple datasets in inversions for anisotropy notably short period group velocity data with strong sensitivity to the crust we present a new whole mantle model of radial anisotropy based on surface wave and body wave travel time data along with incorporated moho perturbations our whole mantle model shares common features with previous global models and is consistent with results from several high resolution regional studies

study of the temporal correlations in the magnitude time series before major earthquakes in japan a characteristic change of seismicity has been recently uncovered when the precursory seismic electric signals activities initiate before an earthquake occurrence in particular the fluctuations of the order parameter of seismicity exhibit a simultaneous distinct minimum upon analyzing the seismic catalog in a new time domain termed natural time and employing a sliding natural time window comprising a number of events that would occur in a few months here we focus on the minima preceding all earthquakes of magnitude 8 and 9 class that occurred in japanese area from 1 january 1984 to 11 march 2011 the day of the m9 tohoku earthquake by applying detrended fluctuation analysis to the earthquake magnitude time series we find that each of these minima is preceded as well as followed by characteristic changes of temporal correlations between earthquake magnitudes in particular we identify the following three main features the minima are observed during periods when long range correlations have been developed but they are preceded by a stage in which an evident anticorrelated behavior appears after the minima the long range correlations breakdown to an almost random behavior possibly turning to anticorrelation the minima that precede m 7 8 earthquakes are distinguished from other minima which are either nonprecursory or followed by smaller earthquakes furthermore it is discussed whether tsallis statistical mechanics in the frame of which it has been suggested that kappa distributions arise can capture the effects of temporal correlations between earthquake magnitudes