wave propagation in heterogeneous porous media a velocity stress finite difference method a particle velocity stress finite difference method is developed for the simulation of wave propagation in 2 d heterogeneous poroelastic media instead of the prevailing second order differential equations we consider a first order hyperbolic system that is equivalent to biot s equations the vector of unknowns in this system consists of the solid and fluid particle velocity components the solid stress components and the fluid pressure a maccormack finite difference scheme that is fourth order accurate in space and second order accurate in time forms the basis of the numerical solutions for biot s hyperbolic system an original analytic solution for a p wave line source in a uniform poroelastic medium is derived for the purposes of source implementation and algorithm testing in simulations with a two layer model additional slow compressional incident transmitted and reflected phases are recorded when the damping coefficient is small this slow compressional wave is highly attenuated in porous media saturated by a viscous fluid from the simulation we also verified that the attenuation mechanism introduced in biot s theory is of secondary importance for fast compressional and rotational waves the existence of seismically observable differences caused by the presence of pores has been examined through synthetic experiments that indicate that amplitude variation with offset may be observed on receivers and could be diagnostic of the matrix and fluid parameters this method was applied in simulating seismic wave propagation over an expanded steam heated zone in cold lake alberta in an area of enhanced oil recovery eor processing the results indicate that a seismic surface survey can be used to monitor thermal fronts

premonitory raise of the earthquakes correlation range lesser antilles abstract we apply to the observed seismicity of lesser antilles a short term earthquake precursor which has been recently found by analysis of synthetic seismicity the latter was generated by a lattice type colliding cascades model of interacting elements precursor named roc depicted premonitory increase of the earthquakes correlation range here this precursor is used as a second approximation to the intermediate term prediction as a first approximation we use the alarms determined in the previous publication by the algorithm seismic reversal sr it depicts premonitory reversal of territorial distribution of seismicity we consider combined performance of both algorithms in prediction of earthquakes with magnitude 5 5 or above four such earthquakes occurred in the territory considered during 1984 1998 the alarms occupy 0 5 of the total time space three alarms happened to be correct two alarms were false and one earthquake was missed by prediction the alarms are very stable to variation of adjustable parameters of prediction method in view of this stability such a prediction is unusually good even for retrospective analysis we present this prediction method as a hypothesis to be tested on advance prediction

acoustic detection of buried objects in 3 d fluid saturated porous media numerical modeling acoustic waves can be a viable tool for the detection and identification of land mines unexplored ordnance uxo and other buried objects design of acoustic instruments and interpretation and processing of acoustic measurements call for accurate numerical models to simulate acoustic wave propagation in a heterogeneous soil with buried objects compared with the traditional seismic exploration high attenuation is unfortunately ubiquitous for shallow surface acoustic measurements because of the loose soil and the fluid in its pore space to adequately model such acoustic attenuation we propose a comprehensive multidimensional finite difference time domain fdtd model to simulate the acoustic wave interactions with land mines and soils based on the biot theory for poroelastic media for the truncation of the computational domain we use the perfectly matched layer pml the method is validated by comparison with analytical solutions unlike the pure elastic wave model this efficient pml fdtd model for poroelastic media incorporates the interactions of waves and the fluid saturated pore space several typical land mine detection measurements are simulated to illustrate the application

elastic waves interacting with buried land mines a study using the fdtd method a three dimensional 3 d finite difference model for elastic waves in the ground has been developed and implemented the model has been created to supplement the development of a sensor that uses elastic waves to detect buried land mines the model is used to investigate the propagation characteristics of elastic waves in the ground and to explore the interaction of elastic waves with buried land mines when elastic waves interact with a buried mine a strong resonance occurs at the mine location the resonance can be used to enhance the mine s signature and to distinguish the mine from clutter results presented in this paper explain the features of elastic wave propagation in the ground and show the interaction of elastic waves with both an anti personnel mine and an anti tank mine

compressional head waves in attenuative formations forward modeling and inversion we develop a method of forward modeling and inverting formation attenuation data from sonic compressional head waves in a fluid filled borehole using a branch cut integration bci technique to calculate individual acoustic arrivals we validate this approach with a real axis integration rai method that does not separate the individual arrivals we show that the straightforward application of the original bci method for lossless media gives erroneous results for attenuative formations with a choice of the riemann sheets satisfying the radiation condition the new bci method gives correct results for most lossy and lossless formations however modeling very slow formations needs to include the contribution of a leaky pole near the vertical branch cut with a constant q assumption we develop a simple processing scheme to extract the formation compressional q factor from the p head wave arrivals we used experimental data from laboratory scale borehole measurements to invert for the compressional q val

reverse tracing of short term earthquake precursors abstract we introduce a new approach to short term earthquake prediction named reverse tracing of precursors rtp since it considers precursors in reverse order of their appearance first we detect the candidates for the short term precursors in our case these are newly introduced chains of earthquakes reflecting the rise of an earthquake correlation range then we consider each chain one by one checking whether it was preceded by an intermediate term precursor in its vicinity if yes we regard this chain as a precursor in prediction it would start a short term alarm the chain indicates the narrow area of possibly complex shape where an intermediate term precursor should be looked for this makes possible to detect precursors undetectable by the direct analysis rtp can best be described on an example of its application we describe retrospective prediction of two prominent californian earthquakes landers 1992 m 7 6 and hector mine 1999 m 7 3 and suggest a hypothetical prediction algorithm this paper descripes the rtp methodology which has potentially important applications to many other data and to prediction of other critical phenomena besides earthquakes in particular it might vindicate some short term precursors previously rejected as giving too many false alarms validation of the algorithm per se requires its application in different regions with a substantial number of strong earthquakes first and positive retrospective results are obtained for 21 more strong earthquakes in california m 6 4 japan m 7 0 and the eastern mediterranean m 6 5 these results are described elsewhere the final validation requires as always prediction in advance for which this study sets up a base we have the first case of a precursory chain reported in advance of a subsequent strong earthquake tokachi oki japan 25 september 2003 m 8 1 possible mechanisms underlying rtp are outlined

comparison between utsu s and vere jones aftershocks model by means of a computer simulation based on the acceptance rejection sampling of von neumann abstract in this research a new algorithm for generating a stochastic earthquake catalog is presented the algorithm is based on the acceptance rejection sampling of von neumann the result is a computer simulation of earthquakes based on the calculated statistical properties of each zone vere jones states that an earthquake sequence can be modeled as a series of random events this is the model used in the proposed simulation contrariwise utsu indicates that the mainshocks are special geophysical events the algorithm has been applied to zones of chile china spain japan and the usa this allows classifying the zones according to vere jones or utsu s model the results have been quantified relating the mainshock with the largest aftershock within the next 5 days which has been named as bath event the results show that some zones fit utsu s model and others vere jones finally the fraction of seismic events that satisfy certain properties of magnitude and occurrence is analyzed

incorporating full attenuation mechanisms of poroelastic media for realistic subsurface sensing porous materials are ubiquitous in the subsurface formations of the earth where acoustic and seismic waves are used for remote sensing however it is not well understood how the dissipation and the dispersion of poroelastic waves are caused by the viscoelastic and viscous properties of the constituents such as solid grains and pore fluid and by the viscoelastic dissipation of the solid frame as well as the viscodynamic coupling of the pore fluid to the solid frame due to its global and local flows relative to the solid grains such attenuation mechanisms have seldom been incorporated in subsurface sensing simulations although they can be very important to applications in this paper we propose a complete attenuation model including both full stiffness and viscodynamic dissipation for poroelastic media in seismic wave simulations completely based on a generalized zener model the effects associated with physical dissipation and frequency dependent dispersion are accurately simulated by a finite difference time domain algorithm verifications with analytical solutions show the accuracy efficiency and flexibility of our method numerical results demonstrate that the attenuation of biot s model in the sediment of the seafloor has significant effects on acoustic wave scattering from complex geologic structures

retrospective on the accelerating seismic release asr hypothesis controversy and new horizons abstract the hypothesis that large earthquakes may be preceded by a period of accelerating seismicity or accelerating seismic release asr was proposed about twenty years ago a compilation of almost one hundred peer reviewed publications on this topic since the late 1980s to the present day shows that the rate of asr studies increased gradually until 2004 but decreased afterwards this negative trend is amplified by a recent increase in the number of negative results and criticisms of the asr hypothesis the author suggests that much of the recent negativity regarding this topic is due to the formulation of this hypothesis as a power law fit to cumulative seismicity series this approach is intrinsically linked to the consensus for criticality evident from an overview of the asr literature to explain the emergence of power laws in earthquake populations the holistic view of the earth s crust as a complex system restricts seismicity pattern analyses to the study of main features such as power laws while a reductionist view would allow for more refined ones such a paradigm shift or sea change might be under way in the asr literature where in 2007 a new approach was proposed to explain the asr power law from combined concepts of elastic rebound and geometry reductionism versus holism is a fundamental problem that not only applies to the study of asr but also to the broader field of earthquake physics and earthquake predictability science

a meddy off cape st vincent part i description abstract a meddy an eddy formed from mediterranean source water was surveyed in detail with two types of expendable profilers and a ctd instrument the muddy comprised two distinct vertically aligned tenses with a combined thickness of 650 m both lenses were stratification minima the upper lens was warmer fresher 12 25 c 36 5 psu and more circular the lower lens was cooler more saline 12 1 c 36 65 psu and more elliptical oriented alone a northeast by southwest line the upper lens homogeneous out to a radius of 6 km had a radius of maximum velocity of 9 km its relative vorticity was 0 85 f and its ertel potential vorticity 4 10 12 m s 1 was 17 times below ambient levels due to the combined effects of negative relative vorticity and vortex stretching the meddy contained more kinetic energy than available potential energy energy burger number of 2 5 compared with historical meddies it had a larger burger number and a more negative vorticity rossby number

the factors related to the occurrence rate of m 4 earthquakes near japanese onshore faults abstract this study investigates which geological and seismicity covariates are most related to the hazard rate along active faults within mainland japan the hazard rate is defined to be the rate of m 4 earthquakes occurring around the fault to investigate the relationship between the hazard rate and the covariates we use cox proportional hazards models each model makes use of all available data by including repeat events large earthquakes that have occurred along the same fault and adjusts for the correlation resulting from the recurrent nature of the data all models show that the recent seismicity rate and length of the fault significantly increase the hazard rate of m 4 earthquakes furthermore we illustrate how the estimated model can be extended to potentially forecast other periods of interest

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

risk and return evaluating reverse tracing of precursors earthquake predictions summary in 2003 the reverse tracing of precursors rtp algorithm attracted the attention of seismologists and international news agencies when researchers claimed two successful predictions of large earthquakes these researchers had begun applying rtp to seismicity in japan california the eastern mediterranean and italy they have since applied it to seismicity in the northern pacific oregon and nevada rtp is a pattern recognition algorithm that uses earthquake catalogue data to declare alarms and these alarms indicate that rtp expects a moderate to large earthquake in the following months the spatial extent of alarms is highly variable and each alarm typically lasts 9 months although the algorithm may extend alarms in time and space we examined the record of alarms and outcomes since the prospective application of rtp began and in this paper we report on the performance of rtp to date to analyse these predictions we used a recently developed approach based on a gambling score and we used a simple reference model to estimate the prior probability of target earthquakes for each alarm formally we believe that rtp investigators did not rigorously specify the first two successful predictions in advance of the relevant earthquakes because this issue is contentious we consider analyses with and without these alarms when we included contentious alarms rtp predictions demonstrate statistically significant skill under a stricter interpretation the predictions are marginally unsuccessful

influence of heterogeneous soils and clutter on the performance of ground penetrating radar for landmine detection ground penetrating radar gpr has been studied for landmine detection and identification since this application employs higher frequencies as compared to conventional largescale gpr measurements the gpr performance is greatly influenced by soil properties and their spatial heterogeneity in order to study the influence of soil heterogeneity on gpr performance three types of soil were investigated from the soil heterogeneity gpr clutter was modeled with the aim of assessing the difficulty encountered in successful gpr performance a handheld dual sensor system that combines a metal detector and gpr was tested in these three test soils and its performance for identifying buried objects was evaluated the gpr performance obtained from the test showed a clear correlation with the modeled gpr clutter hence the present study illustrates that clutter plays a major role in the detection of small objects in heterogeneous soil by gpr

short term earthquake prediction by reverse analysis of lithosphere dynamics abstract short term earthquake prediction months in advance is an elusive goal of earth sciences of great importance for fundamental science and for disaster preparedness here we describe a methodology for short term prediction named rtp reverse tracing of precursors using this methodology the san simeon earthquake in central california magnitude 6 5 dec 22 2003 and the tokachi oki earthquake in northern japan magnitude 8 1 sept 25 2003 were predicted 6 and 7 months in advance respectively the physical basis of rtp can be summed up as follows an earthquake is generated by two interacting processes in a fault network an accumulation of energy that the earthquake will release and a rise of instability triggering this release energy is carried by the stress field instability is carried by the difference between the stress and strength fields both processes can be detected and characterized by premonitory patterns of seismicity or other relevant fields here we consider an ensemble of premonitory seismicity patterns rtp methodology is able to reconstruct these patterns by tracing their sequence backwards in time the principles of rtp are not specific to earthquakes and may be applicable to critical transitions in a wide class of hierarchical non linear systems

seismicity precursors to large earthquakes unified in a stress accumulation framework 1 various seismicity patterns before large earthquakes have been reported in the literature they include foreshocks medium term acceleration and short term activation quiescence doughnut patterns and event migration the existence of these precursory patterns is however debated here we develop an approach based on the concept of stress accumulation to unify and categorize all claimed seismic precursors in a same physical framework we first extend the non critical precursory accelerating seismicity theory n c past which already explains most precursors to additionally include short term activation theoretical results are then compared to the time series observed prior to the 2009mw 6 3 l aquila italy earthquake we finally show that different precursory paths are possible before large earthquakes with possible coupling of different patterns or non occurrence of any this is described by a logic tree defined from the combined probabilities of occurrence of the mainshock at a given stress state and of precursory silent slip on the fault in the case of the l aquila earthquake the observed precursory path is coupling of quiescence and accelerating seismic release followed by activation these results provide guidelines for future research on earthquake predictability

premonitory spreading of seismicity over the faults network in southern california precursor accord 1 we establish a connection between geometry of the faults network in a region and seismicity preceding the strong earthquakes in the intermediate term timescale of years previous studies of observed and computer simulated seismicity demonstrated that strong earthquakes are preceded in that timescale by the rise of seismic activity in a lower magnitude range here we explore a complementary phenomenon spreading of activity over the fault network this phenomenon is depicted by the seismicity pattern accord defined as a simultaneous rise of seismicity in a sufficiently large number of fault zones hence its name pattern accord has been found recently in synthetic seismicity generated by the colliding cascades cc model the present study demonstrates this pattern in observed seismicity of southern california we applied to observations a prediction algorithm based on the pattern accord scaled to the target magnitude 7 5 the pattern accord emerges within a few years before each of the three largest earthquakes in southern california kern county 1952 landers 1992 and hector mine 1999 and at no other time scaled to the target magnitude interval from 6 5 to 7 4 the pattern accord precedes six out of nine earthquakes the duration of alarms in both cases is about 30 of the time considered we repeated prediction with different combinations of adjustable numerical parameters of the algorithm summing up the success and error scores on an error diagram this numerical experiment shows that the prediction results are stable under moderate variations of adjustable parameters the final test would be as always an advance prediction the pattern accord has a simple physical explanation connected with equilibrium of the crustal blocks system under the impact of tectonic driving forces at the same time accord is a manifestation of a broader phenomenon premonitory increase of earthquakes correlation range the latter phenomenon was found for the first time in the cc model although it was hypothesized by one of the authors much earlier

increased correlation range of seismicity before large events manifested by earthquake chains earthquake chains are clusters of moderate size earthquakes which extend over large distances and are formed by statistically rare pairs of events that are close in space and time neighbors earthquake chains are supposed to be precursors of large earthquakes with lead times of a few months here we substantiate this hypothesis by mass testing it using a random earthquake catalog also we study stability under variation of parameters and some properties of the chains we found two invariant parameters they characterize the spatial and energy scales of earthquake correlation both parameters of the chains show good correlation with the magnitudes of the earthquakes they precede earthquake chains are known as the first stage of the earthquake prediction algorithm reverse tracing of precursors rtp now tested in forward prediction a discussion of the complete rtp algorithm is outside the scope of this paper but the results presented here are important to substantiate the rtp approach