noise based monitoring and imaging of aseismic transient deformation induced by the 2006 basel reservoir stimulation abstractwe have analyzed the time dependent properties of the ambient seismic wavefield between 0 1 and 8 hz to detect resolve monitor and image the deformation induced by the water injection associated with the stimulation of the 2006 deep heat mining project in the city of basel switzerland the application of passive methods allowed the detection of an aseismic transient of approximately 35 days duration that began with the onset of the reservoir stimulation peak deformation was reached some 15 days after the bleed off and after the induced seismicity ceased we resolved a significant increase in seismic velocities and a simultaneous decorrelation of the noise correlation coda waveforms the wavefield properties implied that the material response was monitored mainly in the sedimentary layer 2 5 km above the stimulated volume that was approximately 4 5 km deep we inverted the velocity change and decorrelation data to estimate the spatial distribution of the medium changes the resulting imag

volcanic coseismic and seasonal changes detected at white island whakaari volcano new zealand using seismic ambient noise ambient noise interferometry is becoming increasingly popular for studying seismic velocity changes such changes contain information on the structural and mechanical properties of earth systems application to monitoring however is complicated by the large number of processes capable of inducing crustal velocity changes we demonstrate this at white island volcano over a 10 year period containing multiple well documented eruptions using individual seismic stations we detect velocity perturbations that we ascribe to volcanic activity large earthquakes and seasonality distant seismic stations capture widespread nonvolcanic changes that are also present at the volcano comparison between velocity changes recorded by distant and local stations then allows us to distinguish volcanic phenomena from seasonality through this we resolve distinct features in ambient noise derived velocity changes that relate to volcanic unrest and a phreatic eruption illustrating the strength of the approach plain language summary detecting small changes in physical properties at volcanoes is important toward effectively forecasting volcanic eruptions one approach is to monitor the speed of seismic waves at the earth s surface which are sensitive to changes in the rock they pass through at volcanoes such changes may manifest through subsurface pressure increases preceding eruptions correctly interpreting these changes however is complicated many other nonvolcanic processes are also capable of producing similar wave speed perturbations at white island volcano new zealand we detect changes associated with volcanic activity large earthquakes and weather related processes using seismometers located on the volcano we demonstrate that volcanic and nonvolcanic features can be distinguished by comparing changes recorded at the volcano with those recorded at large distances where volcanic changes are not expected to be observed through this we resolve distinct differences that can be related to volcanic activity illustrating the strength of this approach

spurious velocity changes caused by temporal variations in ambient noise frequency content ambient seismic noise cross correlations are now being used to detect temporal variations of seismic velocity which are typically on the order of 0 1 per cent at this small level temporal variations in the properties of noise sources can cause apparent velocity changes for example the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms here we show that if the stretching method is used to measure time shifts then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching with realistic seasonal variations of frequency content in the los angeles basin our numerical tests produce about 0 05 per cent apparent velocity change comparable to what meier et al observed in the los angeles basin we find that the apparent velocity change from waveform stretching depends on time windows and station pair distances and hence it is important to test a range of these parameters to diagnose the stretching bias better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring

understanding of elastic anisotropy of shale under triaxial loading porosity deformation approach abstracttheoretical models for the description of stress dependencies for anisotropic rocks are important for building velocity models and the interpretation of seismic data with respect to stress lithology and pore content especially important is the accurate description of the change of anisotropy due to applied anisotropic stress by means of a quantitative model to aid the interpretation the porosity deformation approach pda originally introduced as the piezosensitivity theory describes stress induced changes of elastic properties without any knowledge about the geometry and orientation of the microcracks we have developed a formulation of the theory for a transverse isotropic rock which was loaded parallel to the bedding plane and we found that it can be described theoretically as an orthorhombic rock we also found out how properties that described the velocity change due to hydrostatic loading can be used to predict elastic anisotropy under additional axial loading the number of free para

detecting seasonal variations in seismic velocities within los angeles basin from correlations of ambient seismic noise summary we analyse 3 yr of continuous seismic records from broad band stations of the caltech regional seismic network ci in vicinity of the los angeles basin using correlations of ambient seismic noise relative velocity variations in the order of 0 1 per cent can be measured between all interstation pairs it is the first time that such an extensive study between 861 interstation pairs over such a large area has been carried out we perform these measurements using the stretching technique assuming that one of the two waveforms is merely a stretched version of the other obviously this assumption is always violated and the two waveforms are generally decorrelated due to temporal changes in the earth crust due to different sources or simply because the cross correlations are not fully converged we investigate the stability of these measurements by repeating each measurement over various time windows of equal length on average between all interstation pairs in the los angeles basin a seasonal signal in the relative velocity variation is observed with peaks and troughs during winter and summer time respectively generally the observed signal decreases with increasing interstation distance and relative traveltime perturbations can only be measured up to an interstation distance of 60 km furthermore the traveltime perturbations do not depend on azimuth of station pairs suggesting that they are not related to seasonal variations of the noise sources performing a simple regionalization by laterally averaging measurements over a subset of stations we found the sedimentary basin showing the most consistent signal and conclude that the observed seasonality might be induced either by changes in the ground water aquifer or thermo elastic strain variations that persist down to a depth of 15 22 km

velocity change in the zone of a moderate mw 5 0 earthquake revealed by autocorrelations of ambient noise and by event spectra a moderate mw 5 0 earthquake occurred near mogul nevada just west of reno nevada on 26 april 2008 this mainshock was surrounded by notable foreshock and aftershock sequences due to the long foreshock sequence the area was well instrumented at the time of the mainshock we investigated the foreshock and aftershock sequences for evidence of velocity changes in the structure immediate to the hypocenter and above it in the area of observed strong ground motion using autocorrelations of the time periods with nearly continuous foreshocks and aftershocks we detected a nearly 1 negative change in velocity on recordings of station mogl which was approximately over the hypocenter of the mainshock we also observed from these recordings a shift in the spectral peaks to lower frequency following the mainshock again indicative of a velocity decrease due to the different spatial sampling of the two methods the effects could not be attributed to the same subsurface volume however both results are strong evidence for coseismic velocity changes accompanying an earthquake which is very much smaller than those for which previous velocity changes have been reported we hypothesize that these changes can be observed for even smaller earthquakes given a fortuitous placement of observing stations

field investigation of frazil jam evolution a case study using field measurements of frazil jams from 1982 to 1989 in the hequ reach of the yellow river this paper discusses both the mechanism of evolution of a frazil jam and the associated variation in water level the variation in water level depends not only on the thickness of the frazil jam but also on the ice discharge an empirical power law relationship between the dimensionless ice thickness and froude number is established it has been found that the critical froude number under an ice cover condition describing the transition from an ice jam to a hanging dam overloaded ice jam is about 0 075 with a dimensionless ice thickness of about 0 4 interestingly the results from the st lawrence river show a similar tendency with similar limits

dynamics of piton de la fournaise volcano observed by passive image interferometry with multiple references abstract activity of piton de la fournaise pdf volcano in la reunion island modifies the seismic velocities within the edifice using the 2010 and 2011 data from a network of 21 seismic stations in the vicinity of pdf changes of seismic velocities are investigated using passive image interferometry i e interferometry of seismic noise correlations as noise correlations change significantly over time in response to volcanic activity a method is presented that allows us to measure continuous long term velocity changes with high and constant accuracy by using multiple periods as reference a long term velocity increase is found that averages about 0 25 per year this trend is superimposed by short term changes that exhibit a clear connection with summit seismo tectonic earthquakes indicating the effect of volcanic activity characteristic signatures of velocity changes are identified for post eruptive periods of deflation that show an increase of velocity associated with subsidence observed by gps periods of pre eruptive inflation are characterized by decreasing velocity seismic crises can be associated with either increasing or decreasing velocity depending on whether the magma movement leads to deflation due to an eruption emptying the shallow plumbing system or to inflation caused by a non eruptive intrusion with a simple assumption about the spatial sensitivity of the measurements both processes are found to have the strongest effect in the central summit area of the volcano which also shows the strongest surface displacements during the time investigated here we do not observe a dependence of the velocity change on the location of the erupting fissures instead the distribution of changes for the three inflation periods and the two eruptions are similar indicating that the velocity changes observed here reflect the dynamics of a shallow magma reservoir rather than the effect of the eruption at the surface

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

new methodology for computing tsunami generation by subaerial landslides application to the 2015 tyndall glacier landslide alaska landslide generated tsunamis pose significant hazards and involve complex multiphase physics that are challenging to model we present a new methodology in which our depth averaged two phase model d claw is used to seamlessly simulate all stages of landslide dynamics as well as tsunami generation propagation and inundation because the model describes the evolution of solid and fluid volume fractions it treats both landslides and tsunamis as special cases of a more general class of phenomena therefore the landslide and tsunami can be efficiently simulated as a single layer continuum with evolving solid grain concentrations and with wave generation via direct longitudinal momentum transfer a dominant physical mechanism that has not been previously addressed in this manner to test our methodology we used d claw to model a large subaerial landslide and resulting tsunami that occurred on 17 october 2015 in taan fjord near the terminus of tyndall glacier alaska modeled shoreline inundation patterns compare well with those observed in satellite imagery

in situ observations of velocity changes in response to tidal deformation from analysis of the high frequency ambient wavefield we report systematic seismic velocity variations in response to tidal deformation measurements are made on correlation functions of the ambient seismic wavefield at 2 8 hz recorded by a dense array at the site of the pinon flat observatory southern california the key observation is the dependence of the response on the component of wave motion and coda lapse time measurements on the vertical correlation component indicate reduced wave speeds during periods of volumetric compression whereas data from horizontal components show the opposite behavior compatible with previous observations these effects are amplified by the directional sensitivities of the different surface wave types constituting the early coda of vertical and horizontal correlation components to the anisotropic behavior of the compliant layer the decrease of the velocity volumetric strain sensitivity s with indicates that this response is constrained to shallow depths the observed velocity dependence on strain implies nonlinear behavior but conclusions regarding elasticity are more ambiguous the anisotropic response is possibly associated with inelastic dilatancy of the unconsolidated low velocity material above the granitic basement however equal polarity of vertical component velocity changes and deformation in the vertical direction indicate that a nonlinear poisson effect is similarly compatible with the observed response pattern peak relative velocity changes at small are 0 03 which translates into an absolute velocity strain sensitivity of s 5 10 3 and a stress sensitivity of 0 5 mpa 1 the potentially evolving velocity strain sensitivity of crustal and fault zone materials can be studied with the method introduced here

seismic velocity change patterns along the san jacinto fault zone following the 2010 m7 2 el mayor cucapah and m5 4 collins valley earthquakes

toward source region tomography with intersource interferometry shear wave velocity from 2018 west bohemia swarm earthquakes the concept of seismic interferometry embraces the construction of waves traveling between receivers or sources with cross correlation techniques in the present study cross correlations of coda waves are used to measure traveltimes of shear waves between earthquake locations for five event clusters of the 2018 west bohemia earthquake swarm with the help of a high quality earthquake catalog i was able to determine the shear wave velocity in the region of the five clusters separately the shear wave velocities range between 3 5 and 4 2 km s the resolution of this novel method is given by the extent of the clusters and better than for a comparable classical tomography it is suggested to use the method in a tomographic inversion and map the shear wave velocity in the source region with unprecedented resolution furthermore the influence of focal mechanisms and the attenuation properties on the polarity and location of the maxima in the cross correlation functions is discussed the intracluster ratio of p wave to s wave velocity is approximately fixed at 1 68

cross correlation analysis of long term ambient seismic noise recordings in the caribbean netherlands to monitor the volcanoes on saba and st eustatius

river ice jams theory case studies and applications the theory of river ice jams as developed by several investigators over the past two decades is reviewed and two methods for analyzing case studies are developed the first method is based on a d

the 2007 m7 7 tocopilla northern chile earthquake sequence implications for along strike and downdip rupture segmentation and megathrust frictional behavior 1 in 2007 a m7 7 earthquake occurred near the town of tocopilla within the northern chile seismic gap main shock slip derived from coseismic surface deformation was confined to the depth range between 30 and 55 km we relocated 1100 events during six months before and one week after the main shock aftershock seismicity is first congruent to the main shock slip and then it spreads offshore west and northwest of mejillones peninsula mp waveform modeling for 38 aftershocks reveals source mechanisms that are in the majority similar to the main shock however a few events appear to occur in the upper plate some with extensional mechanisms juxtaposing the tocopilla aftershocks with those following the neighboring 1995 antofagasta earthquake produces a striking symmetry across an ew axis in the center of mp events seem to skirt around mp probably due to a shallower moho there we suggest that the seismogenic coupling zone in northern chile changes its frictional behavior in the downdip direction from unstable to mostly conditionally stable for both earthquake sequences aftershocks agglomerate in the conditionally stable region whereas maximum inter seismic slip deficit and co seismic slip occurs in the unstable region the boundary between the unstable and conditionally stable zones parallels the coastline we identify a similar segmentation for other earthquakes in chile and peru where the offshore segments break in great m 8 earthquakes and the onshore segments in smaller m 8 earthquakes using critical taper analysis we demonstrate a causal relationship between varying slip behavior on the interface and forearc wedge anatomy that can be attributed to spatial variations in the rate dependency of friction

compressional wave dispersion due to rock matrix stiffening by clay squirt flow the standard biot gassmann theory of poroelasticity fails to explain strong compressional wave velocity dispersion experimentally observed in 12 tight siltstone with clay filled pores in order to analyze and understand the results we developed a new double porosity model of clay squirt flow where wave induced local fluid flow occurs between the micropores in clay aggregates and intergranular macropores the model is validated based on the combined study of ultrasonic experiments on specimens at different saturation conditions and theoretical predictions the presence of a sub pore scale structure of clay micropores contained in intergranular macropores where the fluid does not have enough time to achieve mechanical equilibrium at ultrasonic frequencies and thus stiffens the rock matrix provides a suitable explanation of the experimental data moreover the model provides a new bound for estimating the compressional wave velocity of tight rocks saturated with two immiscible liquids the theoretical predictions indicate that the velocity variation between gas and liquid saturated specimens is predominantly induced by the clay squirt stiffening effect on the rock matrix and not by fluid substitution the effect contributes more than 90 to the variation in the porosity range of 0 5 thus clay squirt flow dominates the relationships between compressional wave velocity and pore fluid in tight rocks

poro acoustoelasticity of fluid saturated rocks we generalize the classical theory of acoustoelasticity to the porous case one fluid and a solid frame and finite deformations a unified treatment of non linear acous toelasticity of finite strains in fluid saturated porous rocks is developed on the basis of biot s theory a strain energy function formed with eleven terms combined with biot s kinetic and dissipation energies yields lagrange s equations and consequently the wave equation of the medium the velocities and dissipation factors of the p and s waves are obtained as a function of the 2nd and 3rd order elastic constants for hydrostatic and uniaxial loading the theory yields the limit to the classical theory if the fluid is replaced with a solid with the same properties of the frame we con sider sandstone and obtain results for open pore jacketed and closed pore jacketed gedanken experiments finally we compare the theoretical results with experimental data

seismic evidence of nonlinear crustal deformation during a large slow slip event in mexico repeated cross correlations of ambient seismic noise indicate a long term seismic velocity change associated with the 2006 m7 5 slow slip event sse in the guerrero region mexico because the sse does not radiate seismic waves the measured velocity change cannot be associated with the response of superficial soil layers to strong shaking as observed for regular earthquakes the perturbation observed maximized at periods between 7 s and 17 s which correspond to surface waves with sensitivity to the upper and middle crust the amplitude of the relative velocity change 10 3 was much larger than the volumetric deformation 10 6 at the depths probed 5 20 km moreover the time dependence of the velocity perturbation indicated that it was related to the strain rate rather than the strain itself this suggests that during strong slow slip events the deformation of the overlying crust shows significant nonlinear elastic behavior

stability analysis of landslide dams under surge action based on large scale flume experiments abstract in recent years large magnitude earthquakes have caused the formation of a large number of landslide dams the rising water level in the landslide lakes may induce a large number of landslides in the lake areas when landslides rush into a lake area large scale surges may be produced and would then strongly impact on the dam stability and cause a breaching process to understand the erosion failure modes of dam bodies caused by surges and the variation in the pore water pressure in the dam body large scale wave flume tests were carried out in this study six groups of comparative tests were carried out to study the two main influencing factors namely the upstream water level and the wave height it was found that 1 when subjected to surge waves the landslide dam stability is determined by the difference h between the effective water level the sum of the water level and the overlapping wave height and the effective dam height the dam height after lowering due to local sliding 2 when h 0 the dam is overtopped and breached by the next waves 3 during dam breach by overtopping with surge waves the erosion in the breach initiation phase is much faster than by overtopping without surge waves but the difference in the breaching development phase is not very significant and 4 the pore water pressure close to the upstream slope is much more sensitive to the action of the surge waves than deeper inside the dam body

river ice break up freeze up a review of climatic drivers historical trends and future predictions river ice plays a fundamental role in biological chemical and physical processes that control freshwater regimes of the cold regions moreover it can have enormous economic implications for river based developments all such activities and processes can be modified significantly by any changes to river ice thickness composition or event timing and severity this paper briefly reviews some of the major hydraulic mechanical and thermodynamic processes controlling river ice events and how these are influenced by variations in climate a regional and temporal synthesis is also made of the observed historical trends in river ice break up freeze up occurrence from the eurasian and north american cold regions this involves assessment of several hydroclimatic variables that have influenced past trends and variability in river ice break up freeze up dates including air temperature indicators e g seasonal temperature 0 c isotherm dates and various degree days and large scale atmospheric circulation patterns or teleconnections implications of future climate change on the timing and severity of river ice events are presented and discussed in relation to the historical trends attention is drawn to the increasing trends towards the occurrence of mid winter break up events that can produce especially severe flood conditions but prove to be the most difficult type of event to model and predict

numerical modeling and experimentation of the dam overtopping process of landslide generated waves in an idealized mountainous reservoir abstracta two dimensional coupled solid fluid numerical model was modified and applied to simulate the dam overtopping event of landslide generated waves in an idealized reservoir the model employed was based on the two dimensional reynolds averaged navier stokes rans in a vertical plane with the k e equations for turbulence closure the motion of the solid landslide was modeled using the equation of motion for rigid body and the free surface was tracked using volume of fluid vof method for model validation experiments were conducted for the case of dam overtopping in an open channel particle image velocimetry piv was used to measure velocity variations of the first wave during dam overtopping in one field of view fov and wave gauges were used to record variations of the free surface elevation at three selected locations in the open channel the calculated and measured data comparisons were performed for time histories of surface elevation surface profile and vertical velocity distribution

coda wave interferometry for estimating nonlinear behavior in seismic velocity in coda wave interferometry one records multiply scattered waves at a limited number of receivers to infer changes in the medium over time with this technique we have determined the nonlinear dependence of the seismic velocity in granite on temperature and the associated acoustic emissions this technique can be used in warning mode to detect the presence of temporal changes in the medium or in diagnostic mode where the temporal change in the medium is quantified

a comparison of methods to estimate seismic phase delays numerical examples for coda wave interferometry time shift estimation between arrivals in two seismic traces before and after a velocity perturbation is a crucial step in many seismic methods the accuracy of the estimated velocity perturbation location and amplitude depend on this time shift windowed cross correlation and trace stretching are two techniques commonly used to estimate local time shifts in seismic signals in the work presented here we implement dynamic time warping dtw to estimate the warping function a vector of local time shifts that globally minimizes the misfit between two seismic traces we compare all three methods using acoustic numerical experiments we show that dtw is comparable to or better than the other two methods when the velocity perturbation is homogeneous and the signal to noise ratio is high when the signal to noise ratio is low we find that dtw and windowed cross correlation are more accurate than the stretching method finally we show that the dtw algorithm has good time resolution when identifying small differences in the seismic traces for a model with an isolated velocity perturbation these results impact current methods that utilize not only time shifts between multiply scattered waves but also amplitude and decoherence measurements

thermoelastic strain in a half space covered by unconsolidated material an algorithm to predict crustal thermoelastic strain from observed local atmospheric temperature is given and applied to a 24 month crustal strain record of one test strainmeter site located near bouquet reservoir in southern california we use a crustal model that consists of an elastically decoupled layer overlying a uniform elastic half space and a thermal source that is given by a stationary temperature wave whose wavelength is related to local topography and or lateral material heterogeneity the decoupled layer delays attenuates and low pass filters the source temperature field the thermoelastic strain in the underlying half space resulting from the temperature variations at the base of the decoupled layer is calculated using the berger 1975 solution for thermoelastic strain in a uniform half space applying our model to the test data we obtain a good fit between predicted and observed strains if we filter the surface thermal signal through a 63 cm thick decoupled layer much of the remaining strain variations clearly correspond to other environmental sources reservoir loading and rainfall our analysis suggests that the horizontal thermoelastic strain is inversely proportional to the wavelength of local topography and or lateral material heterogeneity thus the horizontal thermoelastic strain will be greater in areas of local topography and or lateral material heterogeneity and smaller in more homogeneous and flat areas an upper layer of loose material natural or artificial acts as a thermoelastic strain insulator burial of strainmeters in places where such a layer exists can reduce the thermoelastic strain noise considerably even for shallow strainmeter emplacements

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

seasonal crustal seismic velocity changes throughout japan noise based crustal seismic velocity changes are known to be affected by environmental perturbations such as rainfall atmospheric pressure loading and temperature changes similar to geodetic observations these external perturbations can mask the effects of tectonic and volcanic processes in this study we benefit from the dense hi net short period seismic network that covers the entire japan to measure continuous changes in seismic velocities over a few years using noise based seismic monitoring some strong seasonal seismic velocity changes are observed in both southern japan kyushu island and northern japan hokkaido island decreasing of seismic velocities in summer in southern japan can be clearly explained by a model of increased crustal fluid pore pressure associated with high rainfall in northern japan it is necessary to adopt a more complex model to explain the observed seismic velocity variations which takes into account precipitation snow depth and sea level changes moreover western and eastern hokkaido island show very different responses to these different external perturbations the models developed are used to remove the seasonal components of the seismic velocity changes the minimum remaining detectable seismic velocity change reduces to 10 5 which allows detection of crustal responses to small earthquakes that are previously hidden in the strong seasonal perturbations

stress and mass changes at a wet volcano example during the 2011 2012 volcanic unrest at kawah ijen volcano indonesia since 2010 kawah ijen volcano has been equipped with seismometers and its extremely acid volcanic lake has been monitored using temperature and leveling sensors providing unprecedented time resolution of multiparametric data for an acidic volcanic lake the nature of stress and mass changes of the volcano is studied by combining seismic analyses and volcanic lake measurements that were made during the strongest unrest ever recorded by the seismic network at kawah ijen the distal vt earthquake swarm that occurred in may 2011 was the precursor of volcanic unrest in october 2011 that caused an increase in shallow earthquakes the proximal vt earthquakes opened pathways for fluids to ascend by increasing the permeability of the rock matrix the following months were characterized by two periods of strong heat and mass discharge into the lake and by the initiation of monochromatic tremor mt activity when steam gases interacted with shallow portions of the aquifer significant seismic velocity variations concurrent with water level rises in which water contained a large amount of steam gas were associated with the crises that caused an although the unrest did not affect the shallow hydrothermal system at a large scale whereas shallow vt earthquakes likely reflect a magmatic intrusion mt and relative seismic velocity changes are clearly associated with shallow hydrothermal processes these results will facilitate the forecast of future crises

downstream transition of river ice jams the granular mass theory of river ice jams is extended to their downstream transition as a means of improving understanding of conditions at jam toe the theory is coupled with the equations of motion under and seepage through the jam and the resulting differential equations are solved numerically the present model applies to wide rectangular channels and involves several coefficients whose precise values in nature are unknown example calculations are performed to illustrate the sensitivity of the model to the various coefficients preliminary application of the model to two case studies resulted in plausible findings with regard to grounding of ice jams

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

dynamic ice formation in channels as a driver for stream aquifer interactions 1 this research introduces and provides evidence of a novel mechanism of stream aquifer exchange caused by dynamic ice formation on streams at a stream site in southwestern wisconsin we document a significant fluctuation in stream depth and the potentiometric surface in the adjacent aquifer during periods of ice formation suggesting that stream aquifer interactions may be influenced by these transient events four years of winter stream data document that dynamic ice formation 1 causes an average increase in stream depth of 106 2 affects stream depth on 20 of days from december through february and 3 substantially alters stream aquifer interactions by reducing the hydraulic gradient toward the channel during ice formation events dynamic ice formation represents a potentially widespread mechanism for altering stream aquifer interactions and associated biogeochemical transformations the sensitivity of this process to air temperature indicates a need for further research on the impacts of climate warming

nonlinear acoustoelastic constants of dry and saturated rocks 1 conventional descriptions of the stress dependence of acoustic velocities in rock are often based on microcrack models a more general model independent description that ignores microstructure is third order elasticity theory this theory has had much success in metals and crystals and has recently been applied to rocks as well we measured third order elastic constants in several rocks both dry and water saturated a five velocity measurement technique was used where a rock sample is stressed either hydrostatically or uniaxially and compressional and shear velocities are measured as functions of stress in dry rocks we find that third order elasticity theory provides a good description of velocity versus stress however in water saturated rocks agreement between theoretical predictions and measurements is significantly worse than in dry rocks this indicates that third order elasticity theory does not fully describe the stress dependence of velocities in water saturated rock under our experimental conditions detailed analysis of the velocity data suggests that rock dilatancy may be responsible for the discrepancies between theory and experiment

sudden drop of seismic velocity after the 2004 mw 6 6 mid niigata earthquake japan observed with passive image interferometry 1 passive image interferometry pii is a seismological method employing ambient seismic noise to monitor the temporal evolution of mean shear wave velocity within the earth first the elastic green s tensor between two seismometers is computed from the cross correlation of seismic noise recorded during a certain period second the constructed seismograms of different time periods are treated as earthquake multiplets and small time shifts in their coda are used to invert a relative change in mean shear wave velocity when applied to the source region of the 2004 mw 6 6 mid niigata earthquake japan centroid depth 5 km we used noise recorded at six seismometers located at a distance of less than 25 km from the epicenter daily inversions during the 2 months before and after the earthquake show a sudden drop of mean shear wave velocity of some tenths of a percent at the time of the mid niigata earthquake using noise in two frequency bands 0 1 0 5 hz and 2 8 hz we find similar amplitudes for the velocity drop which indicates that changes are not restricted to the shallow subsurface possible interpretations of this velocity decrease are a decrease of crustal stress after the earthquake a nonlinear site response in the shallow subsurface layer due to strong ground motion or structural weakening due to the creation of new fractures in the source area of the earthquake

time lapse changes of p and s wave velocities and shear wave splitting in the first year after the 2011 tohoku earthquake japan shallow subsurface

a model for seasonal changes in gps positions and seismic wave speeds due to thermoelastic and hydrologic variations it is known that gps time series contain a seasonal variation that is not due to tectonic motions and it has recently been shown that crustal seismic velocities may also vary seasonally in order to explain these changes a number of hypotheses have been given among which thermoelastic and hydrology induced stresses and strains are leading candidates unfortunately though since a general framework does not exist for understanding such seasonal variations it is currently not possible to quickly evaluate the plausibility of these hypotheses to fill this gap in the literature i generalize a two dimensional thermoelastic strain model to provide an analytic solution for the displacements and wave speed changes due to either thermoelastic stresses or hydrologic loading which consists of poroelastic stresses and purely elastic stresses the thermoelastic model assumes a periodic surface temperature and the hydrologic models similarly assume a periodic near surface water load since all three models are two dimensional and periodic they are expected to only approximate any realistic scenario but the models nonetheless provide a quantitative framework for estimating the effects of thermoelastic and hydrologic variations quantitative comparison between the models and observations is further complicated by the large uncertainty in some of the relevant parameters despite this uncertainty though i find that maximum realistic thermoelastic effects are unlikely to explain a large fraction of the observed annual variation in a typical gps displacement time series or of the observed annual variations in seismic wave speeds in southern california hydrologic loading on the other hand may be able to explain a larger fraction of both the annual variations in displacements and seismic wave speeds neither model is likely to explain all of the seismic wave speed variations inferred from observations however more definitive conclusions cannot be made until the model parameters are better constrained

depth sensitivity of seismic coda waves to velocity perturbations in an elastic heterogeneous medium summary numerous monitoring applications make use of seismic coda waves to evaluate velocity changes in the earth this raises the question of the spatial sensitivity of coda wave based measurements here we investigate the depth sensitivity of coda waves to local velocity perturbations using 2 d numerical wavefield simulations we calculate the impulse response at the surface before and after a slight perturbation of the velocity within a thin layer at depth is introduced we perform a parametric analysis of the observed apparent relative velocity changes e obs versus the depth of the thin perturbed layer through the analysis of the decay of e obs we can discriminate two different regimes one for a shallow perturbation and the other for a deep perturbation we interpret the first regime as the footprint of the 1 d depth sensitivity of the fundamental surface wave mode to interpret the second regime we need to model the sensitivity of the multiply scattered body waves in the bulk we show that the depth sensitivity of coda waves can be modelled as a combination of bulk wave sensitivity and surface wave sensitivity the transition between these two regimes is governed by mode conversions due to scattering we indicate the importance of surface waves for the sensitivity of coda waves at shallow depths and at early times in the coda at later times bulk waves clearly dominate the depth sensitivity and offer the possibility of monitoring changes at depths below the sensitivity of the surface waves based on the transition between the two regimes we can discriminate a change that occurs at the surface from a change that occurs at depth this is illustrated for shallow depth perturbations through an example from lunar data

porosity and elastic anisotropy of rocks under tectonic stress and pore pressure changes elastic properties of rocks depend on tectonic stress using the theory of poroelasticity as a constraint we analyze features of these dependencies related to changes in rock pore space geometry we develop a formalism describing elastic moduli and anisotropy of rocks as nonlinear functions of confining stress and pore pressure this formalism appears to agree with laboratory observations to a first approximation elastic moduli and seismic velocities as well as porosity depend only on the difference between the confining tectonic stress and pore pressure however in general both the confining stress tensor and the pore pressure must be taken into account as independent variables the stress dependent geometry of the pore space fully controls the stress induced changes in elastic moduli and seismic velocities specifically the compliant porosity plays the most important role despite the fact that in many rocks the compliant porosity is a very small part of total porosity changes in compliant porosi

noise based seismic monitoring of the campi flegrei caldera the campi flegrei caldera is one of the highest risk volcanic fields worldwide because of its eruptive history and the large population hosted within the caldera it experiences bradiseismic crises sudden uplift with low energetic seismic swarm occurrences no seismicity is recorded out of these deformation rate changes therefore a continuous seismic monitoring of the caldera is possible only by means of the ambient seismic noise we apply a noise based seismic monitoring technique to the cross correlations of 5 year recordings at the mobile seismic network the resulting relative velocity variations are compared to the temporal behavior of the geophysical and geochemical observations routinely sampled at campi flegrei we discriminate between two kinds of crustal stress field variations acting at different timescales they are related to a possible magmatic intrusion and to the gradual heating of the hydrothermal system respectively this study sets up the basis for future volcano monitoring strategies

coseismic and postseismic elastic wave velocity variations caused by the 2008 iwate miyagi nairiku earthquake japan 1 we analyze coseismic and postseismic velocity variations caused by the june 13 2008 iwate miyagi nairiku earthquake mw 6 9 using passive image interferometry pii seismic noise is correlated in order to reconstruct the green s function between two sensors shear wave velocity changes are determined by relating the coda parts of the daily green s functions to a long term reference green s function our study extends from january 2008 to august 2010 and includes the correlations for 190 station pairs in three different frequency ranges from 0 125 to 1 0 hz we show that combining the 9 different component cross correlation functions stabilizes the velocity change estimation and increases analysis resolution the observed velocity change curves can be fitted by model time series consisting of a coseismic velocity drop followed by logarithmic postseismic recovery and seasonal velocity variations the coseismic velocity drops are stronger at higher frequencies and are concentrated in the southern part of the fault zone a tomography algorithm was developed to reproject the observed velocity variations of the different sensor pairs onto the single sensors the depth distribution of coseismic changes was modeled for the three stations with the largest velocity drops at two stations the coseismic velocity changes are located in the upper several hundred meters the third station shows indications for deeper changes in the order of kilometers postseismic recovery takes significantly longer than the analyzed two year period seasonal velocity variations with periods of one year are observed at all analyzed frequencies for most station pairs

comprehensive observation and modeling of earthquake and temperature related seismic velocity changes in northern chile with passive image interferometry we report on earthquake and temperature related velocity changes in high frequency autocorrelations of ambient noise data from seismic stations of the integrated plate boundary observatory chile project in northern chile daily autocorrelation functions are analyzed over a period of 5 years with passive image interferometry a short term velocity drop recovering after several days to weeks is observed for the mw 7 7 tocopilla earthquake at most stations at the two stations pb05 and patcx we observe a long term velocity decrease recovering over the course of around 2 years while station pb05 is located in the rupture area of the tocopilla earthquake this is not the case for station patcx station patcx is situated in an area influenced by salt sediment in the vicinity of salar grande and presents a superior sensitivity to ground acceleration and periodic surface induced changes due to this high sensitivity we observe a velocity response of several regional earthquakes at patcx and we can show for the first time a linear relationship between the amplitude of velocity drops and peak ground acceleration for data from a single station this relationship does not hold true when comparing different stations due to the different sensitivity of the station environments furthermore we observe periodic annual velocity changes at patcx analyzing data at a temporal resolution below 1 day we are able to identify changes with a period of 24 h too the characteristics of the seismic velocity with annual and daily periods indicate an atmospheric origin of the velocity changes that we confirm with a model based on thermally induced stress this comprehensive model explains the lag time dependence of the temperature related seismic velocity changes involving the distribution of temperature fluctuations the relationship between temperature stress and velocity change plus autocorrelation sensitivity kernels

temporal change in shear velocity and polarization anisotropy related to the 2011 m9 0 tohoku oki earthquake examined using kik net vertical array data 1 the m9 0 tohoku oki earthquake took place off ne japan which is covered by a dense seismic network in particular kik net observed the strong motions of the main shock and numerous aftershocks both on the ground and at the bottom of boreholes at a depth of a few hundred meters we applied cross correlation analysis to the coda part of a seismogram observed by kik net and estimated not only the temporal change in shear velocity but also the change in polarization anisotropy between the bottom of the borehole and the ground the shear velocity was suddenly reduced by 5 to 10 after the tohoku oki earthquake over a wide area of ne japan which is consistent with the results of a previous study although some stations also reveal a change in polarization anisotropy the polarization anisotropy change is smaller than the velocity change which may suggest that the static stress change due to the coseismic slip on the pacific plate is not large enough to change the direction of polarization anisotropy and or deviatoric stress in the land area of ne japan

monitoring crustal changes at volcanoes by seismic noise interferometry mt etna case of study abstract in this work we analysed the seismic noise recorded at mt etna by 18 stations during the interval 2007 2015 in the frequency band 0 1 0 3 hz chosen to avoid contamination from volcanic tremor variations in time of medium seismic velocity in the range 0 8 to 0 8 were found mostly affecting the stations located on the volcano summit and flanks based on the investigated frequency content the v v changes took place from the surface to a depth of 4 5 6 5 km to identify the source mechanism of the observed medium changes the variations were quantitatively compared by wavelet transform coherence with volcano tectonic and meteorological parameters a significant relationship with meteorological parameters with seasonal periodicity especially air temperature and snow loading was found probably caused by thermo elastic strain and increasing decreasing surface loading cycles moreover a sharp medium velocity decrease taking place in mid december 2009 and clearly time related to the largest volcano tectonic strain release phenomenon of the investigated period was also found such a velocity decrease was interpreted as resulting from ascent of fluids and gas exsolution taking place at the same time as the volcano tectonic swarm