global earthquake forecasts summary we have constructed daily worldwide long and short term earthquake forecasts these forecasts specify the earthquake rate per unit area time and magnitude on a 0 5 degree grid for a global zone region between 75n and 75s latitude 301 by 720 grid cells we use both the global centroid moment tensor gcmt and preliminary determinations of epicenters pde catalogues like our previous forecasts the new forecasts are based largely on smoothed maps of past seismicity and assume spatial and temporal clustering the forecast based on the gcmt catalogue with the magnitude completeness threshold 5 8 includes an estimate of focal mechanisms of future earthquakes and of the mechanism uncertainty the forecasted tensor focal mechanism makes it possible in principle to calculate an ensemble of seismograms for each point of interest on the earth s surface we also introduce a new approach that circumvents the need for focal mechanisms this permits the use of the pde catalogue that reliably documents many smaller quakes with a higher location accuracy the result is a forecast at a higher spatial resolution and down to a magnitude threshold below 5 0 such new forecasts can be prospectively tested within a relatively short time such as a few years because smaller events occur with greater frequency the forecast s efficiency can be measured by its average probability gains per earthquake compared to the spatially or temporally uniform poisson distribution for the short term forecast the gain is about 2 0 for the gcmt catalogue and 3 7 for the pde catalogue relative to a temporally random but spatially localized null hypothesis preliminary tests indicate that for the long term global spatial forecast the gain is of the order 20 25 compared to the uniform event distribution over the earth s surface we can also prospectively test the long term forecast to check whether it can be improved

seismic slip in the lower crust inferred from granulite related pseudotachylyte in the woodroffe thrust central australia pseudotachylytes generated in granulite facies rocks are found in the woodroffe thrust central australia petrologic evidence and structural and textural features show that these pseudotachylytes contain typical melting origin features including injection occurrence rounded and embayed clasts and microlites within the fine grained matrix which formed contemporaneously with the wall granulite facies rocks under conditions of 8 kbar and 650 700 c these granulite related pseudotachylyte g pt veins are overprinted in subsequent deformation stages by three other types of pseudotachylytes including mylonite related m pt and ultramylonite related um pt pseudotachylytes that are then transcut by cataclasite related pseudotachylytes c pt the overprinting occurred following uplift of the lower crust where the g pt veins formed through the brittle plastic transition zone where the m pt and um pt veins occurred within the brittle dominated regime of the c pt generation zone in the upper crust the coexistence of multiple generations of large voluminous c pt m pt um pt and g pt veins indicates that numerous large earthquakes accompanying distinct seismic slip which produced the pseudotachylytes occurred over an extended period of seismicity and various depths of the crust within the woodroffe thrust zone the spatial distribution and structural features of the multiple stage pseudotachylytes suggest that coseismic slipping caused by large earthquakes which nucleated in the brittle dominated seismogenic zone propagated downward through the brittle plastic transition zone into the plastic dominated granulite facies depth from the upper to lower crust

near field deformation seen on distant broadband seismograms although far field body waves and surface waves are widely recognized the improvements in broadband networks now allow the measurement of near field deformation of large earthquakes at great distances near field motions have been recognized previously only in theory and in close in recordings of earthquakes we show examples from two recent events for the large deep event on june 9 1994 in bolivia there is a clear offset after the arrival of the p wave that has the amplitude expected for the near field term in the shallow september 2 1992 nicaragua earthquake the very long period motion observed between the p and s waves has roughly the amplitude expected from near field terms such near field terms are insensitive to earth structure but supply information on long period source processes and their observation begins to close the gap between long period seismology and geodesy

combination of precise leveling and insar data to constrain source parameters of the mw 6 5 26 december 2003 bam earthquake we used new precise leveling data acquired 40 days after the bam earthquake in combination with radar interferometry observations from both ascending and descending orbits to investigate static deformation associated with the 2003 bam earthquake we invert this geodetic data set to gain insight into the fault geometry and slip distribution of the rupture the best fitting dislocation model is a steeply east dipping right lateral strike slip fault that has a size of 11 by 8 km and strikes n2 w we find that such smooth geometry fits available geodetic data better than previously proposed models for this earthquake our distributed slip model indicates a maximum strike slip of 3 m occurring about 3 to 5 km deep the slip magnitude and depth of faulting taper to the north where the fault approaches the bam city inclusion of crustal layering increases the amount of maximum slip inferred at depth by about 4

comparison of seismic moment release rates along different types of plate boundaries summary this is a global survey of seismic moment release rates scalar moment length time along five categories of plate boundaries for shallow earthquakes we evaluate divergent transcurrent and convergent boundaries for deep earthquakes we consider separately boundaries where the deepest seismicity is intermediate 300 km or deep focus 500 600 km the objective is to evaluate the typical range of rates observed and present the results in a form where it is straightforward to compare factors that affect rates in the different environments for earthquakes occurring 1977 2005 the data are scalar moments from the global centroid moment tensor catalogue for earthquakes 1900 1976 we use a standard formula to obtain moment

shear instability in a viscoelastic material as the cause of deep focus earthquakes the mechanism of deep focus earthquakes has been examined by numerical and linear analysis of shear instability in subducting slabs we assume subducting slabs deform such that the spatially averaged strain rate becomes time independent furthermore we assume that rheology depends on temperature in the manner of an activation process using this model we investigate quantitatively the conditions under which shear instability takes place i e the deformation in the material concentrates in a thin layer whose temperature increases explosively until melting occurs first we study instability in a material whose rheological properties are spatially homogeneous shear instability takes place in a homogeneous material when exceeds a certain critical level e c which depends strongly on the stress in the slabs but does not depend on the detail of the creep law the value of the activation energy next we study instability in a material that contains shear zones similar to those often observed by field geologists i e a thin layer made of material with lower vicosity than the surrounding region we find that shear zones trigger shear instability even for the case of provided that g the ratio of characteristic time of thermal diffusion to that of shear heating in shear zones exceeds 1 and that f the ratio of stiffness of elastic deformation in the surrounding region to that of ductile deformation in shear zones becomes lower than 1 applying this condition to subducting slabs with shear zones we find that shear zones trigger shear instability even when the average strain rate is lower than by an order of magnitude from these results and from an estimate of in subducting slabs we conclude that shear instability is a mechanism likely to induce deep focus earthquakes

on the geometric complexity of earthquake focal zone and fault systems a statistical study we discuss various methods used to investigate the geometric complexity of earthquakes and earthquake faults based both on a point source representation and the study of interrelations between earthquake focal mechanisms we briefly review the seismic moment tensor formalism and discuss in some detail the representation of double couple dc earthquake sources by normalized quaternions non dc earthquake sources like the clvd focal mechanism are also considered we obtain the characterization of the earthquake complex source caused by summation of disoriented dc sources we show that commonly defined geometrical fault barriers correspond to sources without any clvd component we analyze the cmt global earthquake catalog to examine whether the focal mechanism distribution suggests that the clvd component is likely to be zero in tectonic earthquakes although some indications support this conjecture we need more extensive and significantly more accurate data to answer this question fully

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

scaling relations of earthquakes and aseismic deformation in a damage rheology model summary we perform analytical and numerical studies of scaling relations of earthquakes and partition of elastic strain energy between seismic and aseismic components using a thermodynamically based continuum damage model brittle instabilities occur in the model at critical damage level associated with loss of convexity of the strain energy function a new procedure is developed for calculating stress drop and plastic strain in regions sustaining brittle instabilities the formulation connects the damage rheology parameters with dynamic friction of simpler frameworks and the plastic strain accumulation is governed by a procedure that is equivalent to drucker prager plasticity the numerical simulations use variable boundary forces proportional to the slip deficit between the assumed far field plate motion and displacement of the boundary nodes these boundary conditions account for the evolution of elastic properties and plastic strain in the model region 3 d simulations of earthquakes in a model with a large strike slip fault produce scaling relations between the scalar seismic potency rupture area and stress drop values that are in good agreement with observations and other theoretical studies the area and potency of the simulated earthquakes generally follow a linear log log relation with a slope of 2 3 and are associated with stress drop values between 1 and 10 mpa a parameter space study shows that the area potency scaling is shifted to higher stress drops in simulations with parameters corresponding to lower dynamic friction more efficient healing and higher degree of seismic coupling

multiscale brittle ductile coupling and genesis of slow earthquakes we present the first attempt to explain slow earthquakes as cascading thermal mechanical instabilities to attain this goal we investigate brittle ductile coupled thermal mechanical simulation on vastly different time scales the largest scale model consists of a cross section of a randomly perturbed elasto visco plastic continental lithosphere on the order of 100 9 100 km scale with no other initial structures the smallest scale model investigates a km scale subsection of the large model and has a local resolution of 40 9 40 m the model is subject to a constant extension velocity applied on either side we assume a free top surface and with a zero tangential stress along the other boundaries extension is driven by velocity boundary conditions of 1 cm a applied on either side of the model this is the simplest boundary condition and makes it an ideal starting point for understanding the behavior of a natural system with multiscale brittle ductile coupling localization feedback is observed as faulting in the brittle upper crust and ductile shearing in an elasto viscoplastic lower crust in this process brittle faulting may rupture at seismogenic rates e g at 10 2 10 3 ms 1 whereas viscous shear zones propagate at much slower rates up to 3 9 10 9 ms 1 this sharp contrast in the strain rates leads to complex short time scale interactions at the brittle ductile transition we exploit the multiscale capabilities from our new simulations for understanding the underlying thermo mechanics spanning vastly different time and length scales

observations of exotic inner core waves the seismic structure of earth s inner core is highly complex displaying strong anisotropy and further regional variations however few seismic waves are sensitive to the inner core and fundamental questions regarding the origin of the observed seismic features remain unanswered thus new techniques to observe different types of inner core waves are imperative to improve data coverage here we detail our method for detecting exotic inner core phases such as pkjkp and pkiikp using inner core compressional waves as proof of concept we use phase weighted stacking on long period data from a global distribution of stations and employ several synthetic methods including normal mode summation and specfem to identify and confirm the inner core phases we present evidence for two observations of exotic inner core compressional waves and apply the technique to a previously detected inner core shear wave a possible new inner core shear wave remains unconfirmed additionally we show how our method is important for rejecting potential observations and distinguishing between waves with similar traveltime and slowness the method is most successful for detecting exotic inner core compressional waves and will provide a new approach for studying the compressional wave structures in the upper inner core

quasi adiabatic instabilities associated with necking processes of an elasto viscoplastic lithosphere abstract necking of the lithosphere involves complex nonlinear thermal mechanical feedback mechanisms in an elasto viscoplastic plate the mode of extension of such plates relies on the mechanical properties of the upper part of the mantle and on the nucleation of ductile faults within the lithosphere our numerical model addresses the key problem of controls of ductile failure of the strongest part in the lithosphere it is found that a small heterogeneity within this strong part can nucleate quasi adiabatic shear bands these develop spasmodically with time as finite amplitude instabilities with increasing temporal and length scales the largest shear zone takes about 100 000 years to propagate through the entire lithosphere and can lead to a thermal instability for an ambient mantle temperature larger than 900 k in our numerical model thermal runaway occurs when the plate is severed the temperature rise of the thermal instability is a function of the creep law exponent n and can be quenched for a lower n and smaller activation energy the model is applicable to the problem of onset of continental break up and holds the key to ductile instabilities in the earth s lithosphere the changing hot surface temperature on venus might also have precipitated lithospheric instabilities in the past

calculation of static deformation following the bolivia earthquake by summation of earth s normal modes the vertical ground displacement associated with the 9 june 1994 great bolivia earthquake is calculated by summation of earth s normal modes because of the great depth of the earthquake the contributions to the surface displacement field from modes of low radial and angular orders predominate convergence is fast and the truncated mode sum provides a good estimate of the total global displacement field the vertical displacement is calculated to be on the order of 1 cm within a few hundred kill of the epicenter and 1 mm at distances as great as 1500 km normal mode seismograms are calculated for a location near the epicenter and the static offset is seen to occur primarily between the p and s phases consistent with the effect of a near field term the predicted seismograms are in qualitative agreement with the recently reported observations of seismically recorded static displacements on the banjo broadband array jiao et al this issue the static offset calculated in this study is smaller than the observations and predictions reported by jiao et al probably owing to uncertainties in the observations and in their approximate calculations which are based on dislocation theory in an elastic halfspace

a slow earthquake sequence on the san andreas fault earthquakes typically release stored strain energy on timescales of the order of seconds limited by the velocity of sound in rock over the past 20 years observations1 13 and laboratory experiments14 have indicated that rupture can also occur more slowly with durations up to hours such events may be important in earthquake nucleation15 and in accounting for the excess of plate convergence over seismic slip in subduction zones the detection of events with larger timescales requires near field deformation measurements in december 1992 two borehole strainmeters close to the san andreas fault in california recorded a slow strain event of about a week in duration and we show here that the strain changes were produced by a slow earthquake sequence equivalent magnitude 4 8 with complexity similar to that of regular earthquakes the largest earthquakes associated with these slow events were small local magnitude 3 7 and contributed negligible strain release the importance of slow earthquakes in the seismogenic process remains an open question but these observations extend the observed timescale for slow events by two orders of magnitude

mechanics of low angle extensional shear zones at the brittle ductile transition corresponding to low values of the velocity ratio ve vs the 2 d solution for ve vs 1 0 3 reveals the development of a periodic system of extensional shear bands dipping at 30 toward the shearing direction at a depth of 12 to 14 km shear bands are formed after less than half a million years at the base of the reaction zone defined by the region where feldspar to mica reaction is completed shear bands do not propagate to greater depths because the pressure prevents the feldspar from fracturing and thus the reaction to occur the periodic system of shear bands defines a midcrustal flat weakened zone within which the equivalent shear stress is enhanced by at least a factor of three at the shear band tips brittle fracture could thus occur within the midcrustal flat weakened zone explaining therefore the microseismicity monitored at these depths in regions of active extension index terms 8109 tectonophysics continental tectonics extensional 0905 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere 7218 seismology lithosphere and upper mantle 3230 mathematical geophysics numerical solutions keywords continental extension strain localization detachment fault rheology reaction softening numerical model

broadband modeling of local earthquakes three component broadband waveforms of two small earthquakes near upland california recorded on the pasadena broadband high dynamic range instrument were modeled to obtain useful green s functions for this path and to examine the sensitivity of the synthetic seismograms to perturbations of the crustal model we assumed that the source of each event was both simple and known as determined from the caltech usgs array first motions a trapezoidal time function was chosen to fit the width of the direct s wave generalized rays reflectivity and finite difference techniques were used to compute the synthetic seismograms we found that a simple layer over a half space model is an adequate approximation of the upper crust along this profile in particular the waveforms are controlled by a relatively slow 4 km thick surficial layer 4 5km s 1 2 6 km s 1 over a faster layer 5 9 km s 1 3 5 km s 1 the relative amplitudes of direct and multiple s indicate that the main shock occurred at a depth of 6 km while the aftershock occurred at a depth of 8 to 9 km sensitivity analyses indicate that for distances less than 50 km and for periods longer than 1 sec the synthetic seismograms are not very sensitive to perturbations of the deep crustal structure analysis of upper crustal model perturbations revealed that the surficial layer is between 3 to 5 km thick in addition the contact between this layer and the underlying material can be smoothed with a 2 km wide velocity gradient without adversely affecting the fit to the data two dimensional finite difference calculations show that a ridge structure beneath the recorder acts as a lowpass filter the lower frequency phases are largely unaffected other two dimensional models with ridges between the source and receiver clearly did not fit the data synthetic seismograms computed for the best fitting model were used to estimate a long period moment of 6 2 1022 dyne cm ml 4 6 and 1 1022 dyne cm ml 3 7 with identical triangular source time durations of 0 3 sec assuming the same fault dimension of 0 4 km from standard scaling laws stress drop estimates of 410 and 70 bars are obtained for the two events respectively generally we found that it is possible to reproduce local waveforms at frequencies up to 1 hz without a complete knowledge of fine structural detail resulting green s functions can be useful in studying historic events and in simulations of large events from a given source region

source inversion of w phase speeding up seismic tsunami warning w phase is a long period phase arriving before s wave it can be interpreted as superposition of the fundamental first second and third overtones of spheroidal modes or rayleigh waves and has a group velocity from 4 5 to 9 km s 1 over a period range of 100 1000 s the amplitude of long period waves better represents the tsunami potential of an earthquake because of the fast group velocity of w phase most of w phase energy is contained within a short time window after the arrival of the p wave at a distance of 50 w phase energy is contained within 23 min after the origin time which is the distinct advantage of using w phase for rapid tsunami warning purposes we use a time domain deconvolution method to extract w phases from the broad band records of global seismic networks the bandwidth of w phase is approximately from 0 001 to 0 01 hz and we bandpass filter the data from 0 001 to 0 005 hz in most cases having extracted w phase from the vertical component records we perform a linear inversion using a point source to determine mw and the source mechanism for several large earthquakes including the 2004 sumatra andaman earthquake the 2005 nias earthquake the 2006 kuril is earthquake and the 2007 sumatra earthquake w phase inversion yields reliable solutions and holds promise of the use of w phase for rapid assessment of tsunami potential

landslides ice quakes earthquakes a thermodynamic approach to surface instabilities the total rate of rock deformation results from competing deformation processes including ductile and brittle mechanisms particular deformation styles arise from the dominance of certain mechanisms over others at different ambient conditions surprisingly rates of deformation in naturally deformed rocks are found to cluster around two extremes representing coseismic slip rates or viscous creep rates classical rock mechanics is traditionally used to interpret these instabilities these approaches consider the principle of conservation of energy we propose to go one step further and introduce a nonlinear far from equilibrium thermodynamic approach in which the central and explicit role of entropy controls instabilities we also show how this quantity might be calculated for complex crustal systems this approach provides strain rate partitioning for natural deformation processes occurring at rates in the order of 10 3 to 10 9 s 1 we discuss these processes using examples of landslides and ice quakes or glacial surges we will then illustrate how the mechanical mechanisms derived from these near surface processes can be applied to deformation near the base of the seismogenic crust especially to the phenomenon of slow earthquakes

multiple cmt source analysis of the 2004 sumatra earthquake while it is agreed that the great sumatra earthquake of december 26 2004 was among the largest earthquakes of the past century there has been disagreement on how large it was which part of the fault ruptured and how the rupture took place we present a centroid moment tensor cmt analysis of the earthquake in which multiple point sources are used in the inversion to mimic a propagating slip pulse the final model consists of five point sources with the southernmost sources accounting for the majority of the moment release the presumed fault planes of the southern sources strike northwest while those in the north strike northeast consistent with the geometry of the subduction trench slip on the fault is found to be more oblique in the north than in the south the inversion with five sources leads to a moment magnitude for the sumatra earthquake of m w 9 3 consistent with estimates from long period normal mode amplitudes

earthquakes in the ductile regime pseudotachylytes from a crustal scale shear zone in central australia have developed in a cyclical manner once developed an individual pseudotachylyte is deformed in a ductile manner only to be overprinted at a later stage by a new generation of pseudotachylytes such cyclic generation and deformation of pseudotachylyte has been interpreted in the past as representing conditions at the brittleductile transition a different interpretation however is presented here it is proposed that psuedotachylytes and associated ultramylonites can develop entirely within the ductile regime as ductile instabilities such instabilities are different in nature to those previously discussed at length in the geophysical literature but are identical in principle with the instabilities that develop for velocity weakening frictional behavior in spring slider systems at a given strain rate a critical temperature tc is defined at which the transient work hardening equals the product of stress relaxation due to a thermal fluctuation and the heat generated by shearing a necessary condition for ductile instability at a given strain rate is that the temperature is belowtc then the rate of change of stress with respect to strain is negative an additional requirement is that this rate of change exceeds in magnitude the effective elastic stiffness of the loading system ductile instabilities are marginally possible at geological strain rates in quartzites but are possible at mid crustal temperatures in other rock types on the basis of these observations a new interpretation is presented for the base of the seismogenic zone in crustal regions

earthquake source parameters and stress distribution in the adak island region of the central aleutian islands alaska source parameters have been systematically determined for all earthquakes with mw 5 that occurred between 172 w and 179 w longitude in the adak island region of the central aleutian islands during 1977 march 1987 we relocate the events using a plate velocity model developed for the region and use two alternative methods of depth determination the first method uses arrival times of direct and prominent reflected phases primarily pwp the second method uses broadband p wave displacement seismograms in an inversion for source depth the analysis of these events provides a well constrained data set for the study of stress release along an active subduction zone three earthquakes which occurred seaward of the trench axis are located just below the crust mantle interface and show extension nearly perpendicular to the trench axis seven events occurred in the wadati benioff zone sixty four events are located in the main thrust zone and except for five unusual events are characterized by thrust mechanisms with one nodal plane dipping north at a shallow angle in cross section the thrust zone appears as a thin 10 15 km thickness interplate region which extends from 15 to 50 km depth a 10 15 average discrepancy between observed slip vector azimuths and the predicted relative motion direction between the pacific and north american plates exists for these events the observed slip vectors are oriented more normal to the trench than is predicted by plate motions five earthquakes which occurred as aftershocks to the may 7 1986 earthquake mw 8 0 in the crust of the overriding plate have strike slip mechanisms consistent with right lateral motion on arc parallel fault planes observations of slip vectors along the whole aleutian arc show a similar trend to that observed in the adak island region the largest differences 30 between observed and predicted slip azimuths occur around 175 e we propose a model of plate interaction in which a portion of the along arc motion occurs along a weak strike slip shear zone in the upper plate near the volcanic line the slip azimuths in the main thrust zone fit this model well if the amount of transcurrent slip occurring in the upper plate is 60 of the arc parallel relative plate motion a consequence of the model is along arc extension of the overriding plate between the accretionary wedge and the volcanic line especially in the western part of the aleutian arc calculations based on a tectonic model by geist et al 1988 for the formation of arc summit basins through block rotation and translation suggest that along arc extension has been significant since late miocene or early pliocene

upper mantle seismic velocity anomaly beneath southern taiwan as revealed by teleseismic relative arrival times article i nfo probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central taiwan is critical to understanding the local tectonics and orogeny a linear broadband array that transects southern taiwan together with carefully selected teleseismic sources with the right azimuth provides useful constraints they are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths we implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data the resulting patterns of the delayed times systematically vary as a function of the incident angle ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of taiwan combining the ray tracing analysis and a pseudo spectral method to solve the 2 d wave propagations we determine the extent of the anomaly that best fits the observations via the forward grid search the east dipping fast anomaly in the upper mantle beneath the southeast of taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc continent collision is likely characterized by the thin skinned style

experimental and finite difference modelling of borehole mach waves1 abstract a series of model experiments was performed in an ultrasonic laboratory to study the radiation of downhole sources in a variety of formations three models were used in the experiments they were a lucite model a lucite model with a free glass pipe in the centre and a glass cased soil model in addition a finite difference modelling technique was used to simulate the wave propagation in these models and the results of the laboratory and numerical experiments are compared in the lucite borehole model the waveforms recorded in the experiment agree very well with the finite difference synthetics the snapshots of the wavefield from the finite difference simulation show the radiation pattern of the p and s waves in the lucite formation these patterns are consistent with the theoretical calculations in the lucite model with the free glass pipe the finite difference synthetics are also in good agreement with the experimental observations especially for the conical p wave arrival the angle between the wavefront of the conical p wave and the borehole axis observed from the snapshot agrees with the theory in the cased soil model the arrival time of the finite difference synthetics is in good agreement with the laboratory measurements the relative amplitudes of the p wave and the mach wave are not correctly modelled because intrinsic attenuation is not included in the finite difference calculation the mach cone angle from the snapshot agrees with the theoretical prediction finally a finite difference method was used to simulate mach wave propagation in a formation with two horizontal layers in the case of two slow layers the mach wave generated in the first layer is reflected back from and transmitted through the boundary and another mach wave is generated at the second layer when the stoneley wave travels into the second layer in the case of a formation having one slow and one fast layer the mach wave generated in the slow layer is reflected back at the boundary and leaked into the fast layer there is no mach wave in the fast layer

quartz rheology and short time scale crustal instabilities we present numerical results of thermal mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly different character of an olivine mantle in the numerical experiments quartz is found to have a very strong tendency for short time scale instabilities while our numerical experiments show that olivine has a decisive tendency for a stable thermally lubricated slip at the same time olivine can also go through a transitional period of creep bursts which are physically caused by multiple interacting ductile faults at various length and time scales which collocate quickly into a major shear zone since olivine has this strong propensity to self organize in a large apparently stable fault system it lacks the dynamics of interacting ductile faults evident in other minerals quartz behaves totally different and keeps its jerky slip behavior for prolonged deformation an example is shown here in which a 30 50 km piece of a wet quarzitic crust is extended for about 2 ma the associated total displacement field clearly shows the unstable slipping events which have a characteristic time frame of one to several years in contrast olivine is very stable and has a much longer time scale for thermal instability of 100 kyrs

explosive growth of shear heating instabilities in the down slope creep of ice sheets modelisation de la croissance explosive d instabilites de cisaillement thermique d amplitude finie pour la deformation le long des pentes on integre l equation d evolution temporelle du profil vertical de temperature a la suite d un changement brusque de l epaisseur de la glace

introduction to global tsunami science past and future volume ii twenty two papers on the study of tsunamis are included in volume ii of the pageoph topical issue global tsunami science past and future volume i of this topical issue was published as pageoph vol 173 no 12 2016 eds e l geist h m fritz a b rabinovich and y tanioka three papers in volume ii focus on details of the 2011 and 2016 tsunami generating earthquakes offshore of tohoku japan the next six papers describe important case studies and observations of recent and historical events four papers related to tsunami hazard assessment are followed by three papers on tsunami hydrodynamics and numerical modelling three papers discuss problems of tsunami warning and real time forecasting the final set of three papers importantly investigates tsunamis generated by non seismic sources volcanic explosions landslides and meteorological disturbances collectively this volume highlights contemporary trends in global tsunami research both fundamental and applied toward hazard assessment and mitigation

parallel computing of multi scale continental deformation in the western united states preliminary results abstract lithospheric deformation in the western united states is one of the best examples of diffuse continental tectonics that deviate from the plate tectonics paradigm conceptually diffuse continental deformation is known to result from 1 weak and heterogeneous rheology of continents and 2 driving forces that arise from plate boundaries as well as within the continental lithosphere however the dynamic interplay of continental rheology and driving forces hence the geodynamics of continental tectonics remains poorly understood the heterogeneous rheology and multiple driving forces cause continents to deform over different spatiotemporal scales with different physical processes yet most geodynamic models for continental tectonic avoid dealing with such multiphysics partly because of 1 the limited observational constraints of lithospheric structure and deformation and 2 high demands on computing algorithms and resources these constraints however have relaxed significantly in recent years to permit exploration of some of the multi scale physics governing continental tectonics here we present preliminary results of modeling multi scale tectonics in the western united states using parallel finite element computation in a 3d subcontinental scale model we used fine numerical meshes to incorporate all major tectonic boundaries and rheological heterogeneities in the model to explore their interplay with tectonic driving forces in controlling active tectonics in the western us in another model for the entire san andreas fault system we explored strain localization and simulated fault behavior at multi timescales ranging from rupture in seconds to secular fault creep in tens of thousands of years these models can help to integrate data grids with distributed high performance computing resources in the emerging geosciences cyberinfrastructure

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

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

evaluation of nga west2 and chinese ground motion prediction equations for developing seismic hazard maps of mainland chinaevaluation of nga west2 and chinese gmpes for developing seismic hazard maps of mainland china

evidence for static displacements from the june 9 1994 deep bolivian earthquake the 1994 bolivian earthquake mw 8 3 was recorded on scale by 8 very broadband stations deployed approximately 600 km south of the epicenter when these seismograms are carefully converted to ground displacement there appears to be a static offset which is on order of 2 cm we have modeled the waveforms with a synthetic waveform method that contains near intermediate and far field terms although the synthetics are only calculated for an elastic half space they compare favorably with the observed waveform in terms of shape however the theoretical amplitude is 1 2 of the observed static offset which probably reflects the limitations of a homogeneous half space model and or the instabilities in deconvolution

finite difference synthetic acoustic logs the finite difference method is a powerful technique for studying the propagation of elastic waves in boreholes even for the simple case of an open borehole with vertical homogeneity the snapshot format of the method displays clearly the interaction between the borehole and the rock and the origin and evolution of phases we present an outline of the finite difference method applied to the acoustic logging problem including a boundary condition formulation for liquid solid cylindrical interfaces which is correct to second order in the space increments absorbing boundaries based on the formulations of reynolds 1978 and clayton and engquist 1977 were used to reduce reflections from the grid boundaries results for a vertically homogeneous sharp interface model are compared with the discrete wavenumber method and excellent agreement is obtained the technique is also demonstrated by considering sharp and continuous transitions damaged zones at the borehole wall and by considering the effects of wa

frictional melting during the rupture of the 1994 bolivian earthquake the source parameters of the 1994 bolivian earthquake magnitude m w 8 3 suggest that the maximum seismic efficiency was 0 036 and the minimum frictional stress was 550 bars thus the source process was dissipative which is consistent with the observed slow rupture speed only 20 of the locals wave velocity the amount of nonradiated energy produced during the bolivian rupture was comparable to or larger than the thermal energy of the 1980 mount st helens eruption and was sufficient to have melted a layer as thick as 31 centimeters once rupture was initiated melting could occur which reduces friction and promotes fault slip

determination of the fault plane using a single near field seismic station with a finite dimension source model summary we explore the possibility of determining the actual fault plane of an earthquake from the inversion of near source displacement seismograms of one station when a finitedimension source is used instead of a point source model and when the complete displacement is taken into account including near field waves tests on synthetic seismograms and real data recorded at local distances show that this is possible even with a single three component station a single accelerogram available for the erzincan turkey 1992 march 13 m s 6 8 earthquake is inverted and the solution found is compatible with other seismological studies and with the mechanism expected for the north anatolian fault

the tsunami induced by the 2003 zemmouri earthquake mw 6 9 algeria modelling and results summary a strong tsunami with sea disturbances observed along the algerian coast but with significant damage mainly in the balearic islands spain harbours affected the western mediterranean following the 2003 zemmouri earthquake m w 6 9 algeria an average regional uplift of 0 55 m was measured along the shoreline in the epicentral area field observations main shock and aftershocks characteristics are consistent with thrust along a 55 km long rupture trending ne sw dipping se the seismotectonic parameters indicate a hypocentre 7 8 km deep and a possible fault break between 5 and 15 km offshore several tide gauges located in the western mediterranean coast indicated an average of 0 4 m of sea level change with a maximum of 2 m in the balearic islands we generated high resolution bathymetry grids from the algerian coasts to the balearic islands coasts in order to test different seismic sources with different fault rupture location strike and dip and model the tsunami initiation and propagation for the modelling we employed the crank nicolson numerical schema with a finite difference method and the okada elastic dislocation theory for the fault rupture we also highlight the different factors responsible for waves amplification around the balearic coast the best fit between synthetic and real data tide gauges gps levelling and coastal uplift as compared to run up values are obtained for a thrust rupture comparable with the earthquake fault inferred from seismotectonic studies and located within 15 km offshore an analysis of t waves reinforces the earthquake rupture origin for the tsunami this study presents the results and modelling of a major tsunami recorded in the western mediterranean sea

earthquake forecasting in diverse tectonic zones of the globe we present a simple method for long and short term earthquake forecasting estimating earthquake rate per unit area time and magnitude for illustration we apply the method to the pacific plate boundary region and the mediterranean area surrounding italy and greece our ultimate goal is to develop forecasting and testing methods to validate or falsify common assumptions regarding earthquake potential our immediate purpose is to extend the forecasts we made starting in 1999 for the northwest and southwest pacific to include somewhat smaller earthquakes and then adapt the methods to apply in other areas the previous forecasts used the cmt earthquake catalog to forecast magnitude 5 8 and larger earthquakes like our previous forecasts the new ones here are based on smoothed maps of past seismicity and assume spatial clustering our short term forecasts also assume temporal clustering an important adaptation in the new forecasts is to abandon the use of tensor focal mechanisms this permits use of earthquake catalogs that reliably report many smaller quakes with no such mechanism estimates the result is that we can forecast earthquakes at higher spatial resolution and down to a magnitude threshold of 4 7 the new forecasts can be tested far more quickly because smaller events are considerably more frequent also our previous method used the focal mechanisms of past earthquakes to estimate the preferred directions of earthquake clustering however the method made assumptions that generally hold in subduction zones only the new approach escapes those assumptions in the northwest pacific the new method gives estimated earthquake rate density very similar to that of the previous forecast

characteristics of tectonomagmatic earthquake swarms at the southwest indian ridge between 16 e and 25 e summary the ultraslow spreading southwest indian ridge swir is a prominent end member of the global mid ocean ridge system it spreads with a full rate of 14 16 mm y 1 and shows several segments of various obliquities the western swir consists of the oblique and orthogonal supersegments lying at an epicentral distance of 21 to the vna2 seismic array operated by the german neumayer station in east antarctica the array monitors backazimuth apparent velocity and signal to noise ratio of arriving waves and provides a data set of seismicity from the western swir over several years compared to the global seismological network its detection threshold for earthquakes occurring at the western swir is more than 0 5 mb lower enabling a more comprehensive study of mid ocean ridge processes than the teleseismic earthquake catalogues we identified a total number of 743 earthquakes occurring at the western part of the swir and calculated the body wave magnitudes mb from p wave amplitude picks on the vna2 broad band sensor obtaining a magnitude range from mb 3 18 to mb 5 34 in the years of 2001 2004 2005 and 2008 significantly increased event rates indicated four earthquake swarms with up to 164 events lasting for several days all swarms had strong events registered in the international seismological centre catalogue the relocalization of these events confirmed that all swarms occurred in the same region on the orthogonal supersegment we analysed event and moment release rate histories b values and aftershock decay rates modified omori law finding that the swarms of 2001 2004 and 2005 have similarities in the temporal distribution of seismic moment and event numbers the swarm of 2008 is smaller with high magnitude events at the swarm s onset which represent shear failure on normal faults the application of the modified omori law and the b value show that the earthquakes of the swarms do not follow the classical main shock aftershock pattern of purely tectonic earthquake sequences at the orthogonal supersegment a continuous positive magnetic anomaly along the rift axis a negative mantle bouguer anomaly basalts at the seafloor and potentially volcanic edifices indicate robust magmatic crustal accretion the high resolution bathymetry shows ubiquitous rift parallel ridges with steep flanks towards the rift axis indicating high angle normal faults the high magnitude earthquakes detected teleseismically during the swarms are generated there we interpret that the swarms are caused by magmatic accretion episodes at a suggested volcanic centre of the orthogonal supersegment and that possible magma injection activates the steeply dipping fault planes

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

thermoporomechanics of creeping landslides the 1963 vaiont slide northern italy 1 the catastrophic vaiont landslide southern alps italy of 9 october 1963 moved 2 7 108 m3 of rock that collapsed in an artificial lake causing a giant wave that killed 1917 people the landslide was preceded by 2 3 years of creep that ended with the final collapse of the rock mass slipping at about 30 m s 1 assuming that creep was localized in a clay rich water saturated layer in this study we propose shear heating as the primary mechanism for the long term phase of accelerating creep we study only the creeping phase of the slide and we model this phase using a rigid block moving over a thin zone of high shear strain rates introducing a thermal softening and velocity strengthening law for the basal material we reformulate the governing equations of a water saturated porous material obtaining an estimate for the collapse time of the slide our model is calibrated upon real velocity measurements from the vaiont landslide and provides an estimation of the critical time of failure up to 169 days before the collapse we also show that the slide became critical 21 days before the collapse when shear heating started localizing in the clay rich layer inducing a tendency for slip localization and thermal runaway instability in a plane the total loss of strength in the slipping zone during the last minutes prior to the slide is explained by the onset of thermal pressurization triggered by the temperature rise within the clay rich layer

the fluid dynamics of solid mechanical shear zones shear zones in outcrops and core drillings on active faults commonly reveal two scales of localization with centimeter to tens of meters thick deformation zones embedding much narrower zones of mm scale to cm scale the narrow zones are often attributed to some form of fast instability such as earthquakes or slow slip events surprisingly the double localisation phenomenon seem to be independent of the mode of failure as it is observed in brittle cataclastic fault zones as well as ductile mylonitic shear zones in both a very thin layer of chemically altered ultra fine grained ultracataclasite or ultramylonite is noted we present an extension to the classical solid mechanical theory where both length scales emerge as part of the same evolutionary process of shearing the host rock we highlight the important role of any type of solid fluid phase transitions that govern the second degree localisation process in the core of the shear zone in both brittle and ductile shear zones chemistry stops the localisation process caused by a multiphysics feedback loop leading to an unstable slip the microstructural evolutionary processes govern the time scale of the transition between slow background shear and fast intermittent instabilities in the fault zone core the fast cataclastic fragmentation processes are limiting the rates of forming the ultracataclasites in the brittle domain while the slow dynamic recrystallisation prolongs the transition to ultramylonites into a slow slip instability in the ductile realm

analysis of glacial earthquakes in 2003 ekstrom et al reported on the detection of a new class of earthquakes that occur in glaciated regions with the vast majority being in greenland the events have a characteristic radiation pattern and lack the high frequency content typical of tectonic earthquakes it was proposed that the events correspond to large and sudden sliding motion of glaciers here we present an analysis of all 184 such events detected in greenland between 1993 and 2005 fitting the teleseismic long period surface waves to a landslide model of the source we obtain improved locations timing force amplitudes and force directions after relocation the events cluster into seven regions all of which correspond to regions of very high ice flow and most of which are named outlet glaciers these regions are daugaard jensen glacier kangerdlugssuaq glacier helheim glacier the southeast greenland glaciers the northwest greenland glaciers rinks isbrae and jakobshavn isbrae event amplitudes range from 0 1 to 2 0 10 14 kg m force directions are consistent with sliding in the direction of glacial flow over a period of about 50 s each region has a different temporal distribution of events all glaciers are more productive in the summer but have their peak activity in different months over the study period kangerdlugssuaq has had a constant number of events each year whereas jakobshavn had most events in 1998 1999 and the number of events in helheim and the northwest greenland glaciers has increased substantially between 1993 and 2005 the size distribution of events in kangerdlugssuaq is peaked above the detection threshold suggesting that glacial earthquakes have a characteristic size

earthquake near field and w phase observations at teleseismic distances near field phases can be observed on individual broadband seismograms at teleseismic distances from great earthquakes even at distances of 20 30 such phases can have amplitudes of several tenths of a mm while previous studies have identified near field phases in vertical component data i show that such phases can be much more easily observed using the transverse component although observed effects agree well with complete waveform calculations using point moment tensor sources they do not satisfy some of the assumptions commonly made in seismic data analysis it is therefore suggested that care be taken in the analysis of very broadband seismograms which may contain these effects recent w phase observations are shown to be a case in point

initiation of ice ages by creep instability and surging of the east antarctic ice sheet creep or shear heating instability is shown to be a plausible means of initiating a surge of the east antarctic ice sheet and plunging the earth into an ice age the occurrence of this instability requires only that the ice thickness exceed a critical value which may not be much larger than the present ice dome thickness creep instability can occur on the fast time scale of 100 1 000 yr required by inferences of past rapid cooling events and sudden rises of sea level before the onset of northern hemisphere glaciations

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

synthetic seismicity models of multiple interacting faults a synthetic seismicity model for multiple interacting faults of any strike and dip in a three dimensional elastic half space has been developed the ultimate purpose is to determine how hazard is modified by elastic interactions of events in complex fault systems and to examine the synthetic seismicity for unusual behavior before large events that might be observable in the real world each fault is subdivided into some number of equal sized patches and a coefficient of static friction random within a specified range is assigned to each the patch static strength is then the product of friction and differential normal stress stress both shear and normal accumulates due to some predefined tectonic driving force until one or more patches fail and slip instantaneously the slip can be in any direction within the fault plane and its magnitude is determined by a specified fractional stress drop this initial slip induces shear stress and strength changes on all other patches and faults and perhaps results in other patches failing patches can slip more than once once having failed their strength is reduced resulting in an overshoot that approximates the effect of dynamic stress enhancement an event is over when all patches are stable although present computational constraints do not allow models with more than about 1500 patches or a large number of faults experiments with simple models of two parallel strike slip faults 25 km length 15 km depth 694 m x 714 m patch size driven at different rates and separated by 10 or 15 km give some indicative results a range of friction between 0 1 and 0 2 with a stress drop of 10 about 3 mpa or 30 bars produces a b value 500 000 events close to 1 the models generate a distinct class of large characteristic events that rupture the full fault plane the distribution of interevent times for the background seismicity is very similar to that for a poisson process while the characteristic events are quasi periodic nearly half the larger events directly induce some activity on the other fault the effect of a characteristic event on the occurrence of another characteristic event on the opposite fault is small and depends on the separation at 10 km distance other events are retarded while at 15 km distance they are advanced at 10 km separation the probability of a pair of characteristic events within 1 year is reduced to 0 3 from 1 7 for the case with no interaction consideration of interactions between slip on the faults and the driving mechanism as well as higher stress drops and more overshoot would increase the magnitude of the interaction effects

very fast characterization of focal mechanism parameters through w phase centroid inversion in the context of tsunami warning most of the tsunami potential seismic sources in the neam region are in a magnitude range of 6 5 le m w le 7 5 e g the tsunami triggered by the boumerdes earthquake of 2003 with m w 6 9 the centre d alerte aux tsunamis cenalt in operation since 2012 as the french national tsunami warning centre ntwc and candidate tsunami service provider ctsp has to issue warning messages within 15 min of earthquake origin time these warnings are based on the seismic source parameters m w magnitude focal depth and type of fault which are computed by focal mechanisms and centroid inversion methods the w phase method developed by kanamori and rivera allows quick computation of seismic source parameters due to the early arrival time between p waves and surface waves and is therefore particularly useful for monitoring we assess the w phase method with 29 events of magnitude m w ge 5 8 for the period 2010 2015 in the neam region results with 10 min of signal length are in good agreement compared to the global centroid moment tensor gcmt catalog

grain size sensitive flow and shear stress enhancement at the brittle ductile transition of the continental crust localized shear zones along low angle normal faults have been identified in regions of extension at the brittle ductile transition of the continental crust the possibility of the strain localizing at a depth of 10 km is interpreted here as a consequence of an increase in the equivalent shear stress applied to the flow of the lower crust this enhancement of the flow stress is seen as a prerequisite for the triggering of brittle deformation mechanisms leading to strain localization the lower crust rheology used to examine this stress increase is strain rate temperature and grain size dependent due to the coupling of dislocation and diffusion creep the model structure proposed consists of a top layer the upper crust gliding rigidly above a bottom layer the lower crust which deforms in simple shear during a short time interval 1400 years the equivalent shear stress is found to increase by a factor of up to 3 67 mpa for anorthite and 17 mpa for quartz for anorthite this stress could explain the activation of a mohr coulomb failure with a friction coefficient of 0 2 which is reasonable at the depth of 10 km dislocation creep is activated during a rapid change in the prescribed velocity whereas diffusion creep dominates if the velocity is held constant highlighting the importance of grain size sensitivity for lower crustal rheology

modeling shear zones in geological and planetary sciences solid and fluid thermal mechanical approaches abstract shear zones are the most ubiquitous features observed in planetary surfaces they appear as a jagged network of faults at the observable brittle surface of planets and in geological exposures of deeper rocks they turn into smoothly braided networks of localized shear displacement leaving centimeter wide bands of mylonitized reduced grain sizes behind the overall size of the entire shear network rarely exceeds kilometer scale at depth although mylonitic shear zones are only visible to the observer when uplifted and exposed at the surface they govern the mechanical behavior of the strongest part of the lithosphere below 10 15 km depth mylonitic shear zones dissect plates thus allowing plate tectonics to develop on the earth we review the basic multiscale physics underlying mylonitic ductile shear zone nucleation growth and longevity and show that grain size reduction is a symptomatic cause but not necessarily the main reason for localization we also discuss a framework for analytic and numerical modeling including the effects of thermal mechanical couplings thermal elasticity the influence of water and void volatile feedback the physics of ductile shear zones relies on feedback processes that turn a macroscopically homogenously deforming body into a heterogeneously slipping solid medium positive feedback can amplify strength heterogeneities by cascading through different scales we define basic intrinsic length scales of strength heterogeneity such as those associated with plasticity grain size fluid inclusion and thermal diffusion length scale for an understanding ductile shear zones we need to consider the energetics of deformation shear heating introduces a jerky flow phenomenon potentially accompanied by ductile earthquakes additional focusing due to grain size reduction only operates for a narrow parameter range of cooling rates for the long time scale deformational energy stored inside the shear zone through plastic dilation or crystallographic and shape preferred orientation consumes only a maximum of 10 of energy dissipated in the shear zones but creates structural anisotropy shear zones become long living features with a long term memory a special role is attributed to the presence of water in nominally anhydrous minerals we show that water directly affects the mechanical equation of state and has the potential to synchronize viscous and plastic flow processes at geological time scale we have shown that fully coupled finite element calculations using mechanical data from the laboratory can reproduce the basic mode of deformation of an entire mylonitic shear zone the next step of modeling lies in benchmarking basic feedback mechanism in field studies and zooming into the braided network of shear zone structure without losing the large scale constraint numerical methods capable of fulfilling the goal are emerging these are adaptive wavelet techniques and hybrid particle finite element codes which can be run over a computational grid across the net

w phase source inversion for moderate to large earthquakes 1990 2010 rapid characterization of the earthquake source and of its effects is a growing field of interest until recently it still took several hours to determine the first order attributes of a great earthquake e g m w 7 5 even in a well instrumented region the main limiting factors were data saturation the interference of different phases and the time duration and spatial extent of the source rupture to accelerate centroid moment tensor cmt determinations we have developed a source inversion algorithm based on modelling of the w phase a very long period phase 100 1000 s arriving at the same time as the p wave the purpose of this work is to finely tune and validate the algorithm for large to moderate sized earthquakes using three components of w phase ground motion at teleseismic distances to that end the point source parameters of all m w 6 5 earthquakes that occurred between 1990 and 2010 815 events are determined using federation of digital seismograph networks global seismographic network broad band stations and sts1 global virtual networks of the incorporated research institutions for seismology data management center for each event a preliminary magnitude obtained from w phase amplitudes is used to estimate the initial moment rate function half duration and to define the corner frequencies of the passband filter that will be applied to the waveforms starting from these initial parameters the seismic moment tensor is calculated using a preliminary location as a first approximation of the centroid a full cmt inversion is then conducted for centroid timing and location determination comparisons with harvard and global cmt solutions highlight the robustness of w phase cmt solutions at teleseismic distances the differences in m w rarely exceed 0 2 and the source mechanisms are very similar to one another difficulties arise when a target earthquake is shortly e g within 10 hr preceded by another large earthquake which disturbs the waveforms of the target event to deal with such difficult situations we remove the perturbation caused by earlier disturbing events by subtracting the corresponding synthetics from the data the cmt parameters for the disturbed event can then be retrieved using the residual seismograms we also explore the feasibility of obtaining source parameters of smaller earthquakes in the range 6 0 mw 6 5 results suggest that the w phase inversion can be implemented reliably for the majority of earthquakes of mw 6 or larger

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

scardec a new technique for the rapid determination of seismic moment magnitude focal mechanism and source time functions for large earthquakes using body wave deconvolution accurate and fast magnitude determination for large shallow earthquakes is of key importance for post seismic response and tsumami alert purposes when no local real time data are available which is today the case for most subduction earthquakes the first information comes from teleseismic body waves standard body wave methods give accurate magnitudes for earthquakes up to mw 7 7 5 for larger earthquakes the analysis is more complex because of the non validity of the point source approximation and of the interaction between direct and surface reflected phases the latter effect acts as a strong high pass filter which complicates the magnitude determination we here propose an automated deconvolutive approach which does not impose any simplifying assumptions about the rupture process thus being well adapted to large earthquakes we first determine the source duration based on the length of the high frequency 1 3 hz signal content the deconvolution of synthetic double couple point source signals depending on the four earthquake parameters strike dip rake and depth from the windowed real data body wave signals including p pcp pp sh and scs waves gives the apparent source time function stf we search the optimal combination of these four parameters that respects the physical features of any stf causality positivity and stability of the seismic moment at all stations once this combination is retrieved the integration of the stfs gives directly the moment magnitude we apply this new approach referred as the scardec method to most of the major subduction earthquakes in the period 1990 2010 magnitude differences between the global centroid moment tensor cmt and the scardec method may reach 0 2 but values are found consistent if we take into account that the global cmt solutions for large shallow earthquakes suffer from a known trade off between dip and seismic moment we show by modelling long period surface waves of these events that the source parameters retrieved using the scardec method explain the observed surface waves as well as the global cmt parameters thus confirming the existing trade off for some well instrumented earthquakes our results are also supported by independent studies based on local geodetic or strong motion data this study is mainly focused on moment determination however the scardec method also informs us about the focal mechanism and source depth and can be a starting point to study systematically the complexity of the stf

elastic wave propagation in a fluid filled borehole and synthetic acoustic logs the propagation and dispersion characteristics of guided waves in a fluid filled borehole are studied using dispersion curves and modeling full wave acoustic logs by synthetic microseismograms the dispersion characteristics of the pseudo rayleigh reflected and stoneley waves in a borehole with and without a tool in the center are compared effects of different tool properties are calculated the effect of a rigid tool is to make the effective borehole radius smaller as an approximation dispersion characteristics of the guided waves in a borehole with a tool can be calculated as a purely fluid filled borehole with a smaller effective radius theoretical waveforms microseismograms of elastic waves propagating in a borehole are calculated using a discrete wavenumber integration with an appropriate choice of parameters our results look similar to the acoustic waveforms recorded in a limestone and a shale formation several factors affect the shape of an acoustic log microseismogram the effective rad

estimate of the tsunami source of the 1992 nicaraguan earthquake from tsunami data the nicaraguan earthquake of september 2 1992 excited large tsunamis which caused significant damage along the nicaraguan coasts some of the inhabitants felt only minimal shock before the tsunami arrived indicating that excitation of short period seismic waves was very small numerical simulation with the initial tsunami source estimated by the seismic data is carried out to study the characteristics of the tsunami source by comparing the calculated data with the measured data along the nicaraguan coast finding of the comparison shows that the dislocation of the fault estimated from the measured data is 5 6 to 10 0 times larger than that from seismic data the tsunami source area which is 200km in length 100km in width is used to explain the distribution of measured tsunami heights along the coast and the wave period as shown in the tide record at corinto the effect of rise time on tsunami excitation indicates a slow process which corresponds with the seismic waves this event falls under the tsunami earthquake category to produces anomalously large tsunamis relative to earthquake magnitude

generation of intermediate depth earthquakes by self localizing thermal runaway the conditions leading to rock failure during intermediate depth earthquakes in subduction zones are not clear particularly in the absence of free fluid field observations and numerical simulations indicate that thermal weakening due to high temperature shear instabilities may trigger earthquakes under such circumstances intermediate depth 50 300 km earthquakes commonly occur along convergent plate margins but their causes remain unclear in the absence of pore fluid pressures that are sufficiently high to counter the confining pressure in such settings brittle failure is unlikely in such conditions the rocks could fail by the mechanism of progressively self localizing thermal runaway1 whereby ductile deformation in shear zones leads to heating thermal softening and weakening of rock1 2 3 here we test this hypothesis by focusing on fault veins of glassy rock pseudotachylyte formed by fast melting during a seismic event as well as associated ductile shear zones that occur in a precambrian terrane in norway our field observations suggest that the pseudotachylytes as well as shear zones have a single event deformation history and we also document mineralogical evidence for interaction of the rocks with external fluids using fully coupled thermal and viscoelastic models we demonstrate that the simultaneous occurrence of brittle and ductile deformation patterns observed in the field can be explained by self localizing thermal runaway at differential stresses lower than those required for brittle failure our results suggest that by perturbing rock properties weakening by hydration also plays a key role in shear zone formation and seismic failure however thermal runaway enables the rocks to fail in the absence of a free fluid phase

surface wave tomography of the upper mantle beneath the reykjanes ridge with implications for ridge hot spot interaction 1 we modeled fundamental mode love and rayleigh waves to study the seismic properties of the upper mantle beneath the reykjanes ridge these waves were generated by regional earthquakes occurring in the north atlantic to the south of iceland and were recorded by stations located on iceland over 12 000 measurements of the phase group arrival time and amplitude of narrow pass filtered waveforms over the period range of 9 5 100 s were used to solve for mantle shear wave velocity structure and anisotropy in a vertical plane oriented normal to the ridge axis the velocity structure contains a broad and deep low velocity zone in the upper mantle beneath the ridge a joint analysis of the seismic structure with gravity data reveals that the low velocities are consistent with elevated temperatures 75 our study shows that plume material spreads broadly outward beneath the reykjanes ridge from iceland and is not confined to a narrow lithospheric channel at distances 200 km from the ridge shear wave anisotropy indicates a predominant horizontal alignment of the fast axes of anisotropic crystals mainly above 50 km depth which can be interpreted as past horizontal ridge perpendicular flow within 200 km of the ridge the anisotropy indicates a general vertical alignment of the fast axes or an alignment such that the fast axes point along the ridge the transition to this type of anisotropy coincides with the appearance of increased hot spot ridge interaction 20 myr ago indicating that plume flow has largely disrupted mantle flow beneath the ridge since that time

rupture process of the april 24 2017 mw 6 9 valparaiso earthquake from the joint inversion of teleseismic body waves and near field data abstract the central chilean margin 32 33 s is characterized by the subduction of the juan fernandez ridge jfr beneath the continental south american plate the jfr corresponds to a hotspot track composed by seamounts typically 3 3 5 km high above the surrounding seafloor with a ridge trench collision zone underlying the prominent valparaiso forearc basin vfb this region has been affected by several large and mega earthquakes where the last event corresponds to a complex seismic sequence that took place at the southern edge of vfb in april 2017 the spatio temporal distribution of the seismic events is characterized by a predominant southeast migration of the seismicity an mw 6 9 earthquake triggered two days after the sequence started and occurred at the northern end of the rupture area of the 1985 mw 8 0 valparaiso earthquake we compute the kinematic rupture process of the 2017 mw 6 9 valparaiso earthquake from the joint inversion of teleseismic body waves and near field data the akaike s bayesian information criterion was used to objectively estimate both the relative weighting between datasets and the weighting of spatial and temporal constraints used as a priori information the coseismic slip is distributed over an area of dimensions 35 10 km2 with a maximum slip of 1 5 m the rupture propagated unilaterally downdip the source duration from the moment rate solution is 20 s with a total seismic moment of 3 05 1019 nm mw 6 9 the analysis of the seismicity shows that most of the events occurred along the plate interface foreshock clustered northern from the mainshock epicenter and the aftershocks occurred to the southeast at a deeper location the inverted regional moment tensors show similar faulting mechanism than the mainshock the seismic sequence started two days before the mainshock and lasted for about two weeks and a migration pattern of the seismicity was observed the rupture of the 2017 mw 6 9 earthquake nucleated where the san antonio seamount belonging to the jfr is subducting and propagated downwards along a zone that presents high interseismic coupling the complex seismic sequence might be explained by an aseismic slip transient in the zone and the influence of the downdip migration of fluids from the accretionary prism along the subduction channel the erosive and tunneling effect left by the sudden slip of the subducting seamount might provide the cavity for downdip migration of fluids and subsequent swarm seismicity