NG31A-0844 0800h
Integration of Remote Sensing and Seismic data in Active Fault Regions
Global Positioning System (GPS) data is now widely used to observe and measure tectonic motion in active fault regions. New analysis techniques have demonstrated that relatively small signals on a variety of spatial and temporal scales can be detected and modelled in this data (Tiampo et al., 2004). In addition, applications from the field of phase dynamics are being used to study the underlying physics of the fault system using historical seismicity data (Tiampo et al., 2002). Here we integrate these two data types with Moderate Resolution Imaging Spectroradiometer (MODIS) data in an attempt to link the changes in deformation and seismicity with heat flow changes detected via satellite.
NG31A-0845 0800h
Connecting the Microscale to the Macroscale in Earthquake Processes: Scaling and its Relationship to Nucleation in Damage Mechanics
The process of earthquake initiation and failure typically involves a range of scales, inasmuch as the foreshocks and aftershocks are significantly smaller in magnitude than the mainshock. The physics of these processes are similar to the processes involved in damage mechanics in materials, which can be studied in the laboratory. Material damage occurs when microscopic processes of dislocation dynamics and microcrack formation are produced in association with strain and fracture mechanisms operating on the macroscopic scale. Here we discuss the physics of self-organization and damage at the "microscopic" scale, and how it relates to the "macroscopic" scale of the fracture. We begin by writing a free energy functional that connects the microscale with the macroscale processes. Since damage represents a modification of a brittle elastic system, we expect to find that the interactions produce the mean field dynamics characteristic of elastic systems. Sudden transitions in the state of these systems can be understood in the context of first order phase transitions, where the influence of the classical limit of stability, or spinodal, is felt. The appearance of a mean field spinodal leads to a general coarse-grained equation, which expresses the balance between rate of stress supplied, and rate of stress dissipated in the processes leading to surface damage. We can use ideas from thermodynamics and kinetics of phase transitions to develop the form of standard equations for material damage, giving clear physical meaning to all terms and variables. Ultimately, the self-organizing dynamics arise from the appearance of an energy landscape in these systems, which in turn arises from the strong correlations and mean field nature of the physics. We demonstrate that these ideas lead to dynamical equations, and we derive the scaling properties of the solutions. Our theory has the novel feature that, while the initial nucleation process occurs in a non-classical spinodal mode, the final crack or "droplet" has a classical profile, as a result of the decreasing range of interaction as damage increases. We also compare with laboratory data and show reasonable agreement in certain cases.
NG31A-0846 0800h
Application of ensemble Kalman filter to coupled atmosphere-ocean model
We apply the ensemble Kalman filter (EnKF) to the coupled ocean-atmosphere model by Zebiak and Cane (ZC model, Zebiak and Cane [1987]) in order to assimilate the TOPEX/Poseidon sea surface height (SSH) observation. Since the ZC model includes several nonlinear processes, it is impossible to use the standard Kalman filter and smoother algorithms. We therefore employ the EnKF in which the Kalman gain is approximately estimated by many realizations of the state vector. Here we add process noise to the bulk formula that converts the atmospheric wind into the windstress on the sea. The filtered SSH roughly appears similar to the observation, but it is contaminated by a false stripe structure near the eastern boundary. The false stripe then propagates westward to make the model prediction get worse. This stripe is caused by the specified eastern boundary condition that induces an extremely large Kalman gain there. To avoid the contamination, we propose alternative filtering schedules in the coupled process and a possibility of another filtering method.
NG31A-0847 0800h
Continuous Monitoring of Groundwater on Monferrato Area (Piemonte, North Italy): Correlation Analysis Between Seismic Events and Geochemical Variations
Variations in the chemical-physical and geochemical parameters of groundwater correlated to seismic and volcanic activity were wide documented by several authors (Carapezza et al., 1980; Capasso et al., 1991; Tedesco et al.; 1995; Gurrieri & Valenza 1988; Sano et al., 1998; Gurrieri & Giudice 2004). According to these results a project for groundwater geochemical surveillance has been started in Monferrato area (Piemonte north Italy). Since August 2000 this area was characterized by seismic activity with earthquake intensity up to 5.2 Md. Other seismic events of lower magnitude were also reordered. Some geochemical anomalies were observed in groundwater at the occurrence of the seismic activity (Quattrocchi et al., 2003). In may 2004, a network for continuous monitoring was installed. It consists of four geochemical continuous monitoring stations placed close to Nizza-Monferrato town (At). The stations are able to recorder, hourly, water temperature, pH, electrical conductivity, piezometric level and the main atmospheric parameters such as T, P, Rain, RU, Speed and Wind Direction. A first thermo anomaly was noted in a hand excavate well denoted as Ronello. The water start to heating since June, 8, 2004, and its temperature rises from 13 to $18\deg$C in four days. Nine days after, on June, 17, 2004, a seismic event of 2.8 Md occurred. In the subsequent months both the temperature and conductivity show very complex trend, likely due to the stress field persistence. During the August month the temperature roughly decrease from 34 to $18\deg$C and then rise sharply until $25\deg$C. This anomalous behaviour precedes a new seismic events of Md 2.6 occurred on September, 09, 2004.
NG31A-0848 0800h
Nonlinear Prediction of Atlantic Hurricane Abundance in 2004 Season
Hurricanes are an eddy phenomenon in the weather system. Each year hurricanes form out of the global atmosphere circulation in a couple of months and then disappear. One of the directions in hurricane research is to discuss the characteristics of annual hurricane behavior in order to answer questions such as how many hurricanes may occur in a coming hurricane season (i.e., the hurricane annual abundance or frequency) and how long they will last (i.e., the hurricane duration) [1]. Usually the historical best track data are utilized for analysis of the climatology of hurricane seasons. The time series of the annual abundance of North Atlantic hurricanes over the period 1886-2003 [2] shows a series of bursty data with self similarity, which suggests that a nonlinear prediction method based on fractal dimension may be good to describe the abundance of hurricane season in 2004. This paper tries to use F4 [3] - a nonlinear prediction method based on fractal dimension to forecast the number of hurricanes in 2004 season. The hurricanes annual frequency in the Atlantic basin from 1886 to 2003 is extracted from the NHC best track data [2]. The whole series contains 118 data points. A set of experiments is designed as followed. A 2004 estimate is computed by F4 using all the 118 data points. That is, the whole data series from 1886 to 2003 is used to forecast the number in 2004. A second estimate is computed by F4 using the series from 1886 to 2002, totally 117 data points. Of course F4 will produce estimates of the number of hurricanes in both 2003 and 2004 seasons. The idea is to test F4 estimate with the actual observation in the 2003 season at the mean time to make a forecast of the 2004 season. This idea can be applied where the series from 1886 to 2001, to 2000, to 1999, until to 1994 are used respectively to make estimates till 2004. Overall, F4 states that there will be 6-7 hurricanes in the Atlantic basin for this 2004 season. References: [1] James B. Elsner and A. Birol Kara, Hurricanes of the North Atlantic: Climate and Society, Oxford University Press, June 1, 1999, ISBN: 0195125088. [2] NHC/TPC archive, http://www.nhc.noaa.gov/pastall.shtml, last accessed on Sep 09 2004. [3] Deepay Chakrabarti and Christos Faloutsos, 2002, F4: Large-scale Automated Forecasting Using Fractals, in Proceedings of the 2002 ACM CIKM International Conference on Information and Knowledge Management (CIKM 2002), McLean, VA, USA, November 4-9, 2002, pp 2-9.
NG31A-0849 0800h
A model for inter-occurrence time distribution of aftershocks
Earthquakes are characterized by several scaling laws. These laws are defined in temporal and spatial domains and are manifestations of underlying nonlinear irreversible dynamics of the upper brittle crust. In this work we study the temporal decay rates of aftershock sequences of major California earthquakes and propose a generalized law incorporating the three empirical laws: the Gutenberg-Richter relation, Omori's law for the temporal evolution of aftershocks, and the modified Bath's law for the difference between the magnitudes of a main shock and its largest aftershock. We also study the inter-occurrence time distribution between earthquakes and introduce a model based on a non-homogeneous Poisson process (NHPP) to quantify the observed scaling. In this model we employ the generalized Omori's law for the decay of aftershocks as a time dependent rate in NHPP. We also examine the stretched-exponential rate derived from the mean-field approximation to earthquake processes as a time dependent rate in NHPP. Using the analytically derived distribution of inter-occurrence times, we apply this scaling to several major aftershock sequences in California to confirm the validity of our hypothesis. We argue that the NHPP combined with the generalized Omori's law or the stretched-exponential rate can be used to quantify the observed temporal scaling of inter-occurrence times between earthquakes.
NG31A-0850 0800h
Time-step sensitivity of nonlinear atmospheric models: numerical convergence, truncation error growth and ensemble design
Computational models based on discrete dynamical equations are a successful way of approaching the problem of predicting or forecasting the future evolution of dynamical systems. For linear and mildly non-linear models, the solutions of the numerical algorithms in which they are based, converge to the analytic solutions of the underlying differential equations, for small time-steps and grid-sizes. In this paper, we investigate the time-step sensitivity of three non-linear atmospheric models of different levels of complexity: the Lorenz equations, a quasi-geostrophic (QG) model and a global weather prediction system (NOGAPS). We show that for chaotic systems, numerical convergence cannot be guaranteed forever. The decoupling of solutions for different time-steps follows a logarithmic rule similar for the three models. In regimes that are not fully chaotic, the Lorenz equations are used to show that different time-steps may lead to different model climates and even different regimes. We propose a simple model of truncation error growth in chaotic systems that reproduces the behavior of the QG model error growth for different time-steps. Experiments with NOGAPS suggest that truncation error is a substantial component of total forecast error of the model. Ensemble simulations with NOGAPS show that using different time-steps is a simple and natural way of introducing an important component of model error in ensemble design.
NG31A-0851 0800h
An aid to making subsurface hydrology predictive
Especially as concerns unsaturated media, the current state of subsurface modeling is to use standard partial differential equations with constitutive relationships chosen to minimize interference with smooth numerical recipes. Boundary conditions are handled logically, but heterogeneity is not. The constitutive relationships contain parameters, which have no known relationship to geology or soil conditions. Simple predictions of the hydraulic conductivity in (nominally) homogeneous media using these relationships typically fail by orders of magnitude, so in heterogeneous applications researchers conduct sensitivity studies to see, which parameter has been misunderstood, and make unjustifiable inferences regarding the relationships between the medium and the parameter. Alternatively, one can calculate the constitutive relationships from first principles. Here I show how to obtain expressions for the unsaturated hydraulic conductivity, the air permeability, and the electrical conductivity. Comparison with experiment demonstrates not only that the theory is predictive, but, also that the model (truncated random fractals) is sound. The difficulty with these expressions is that they are based on percolation theory. Since near saturation the air phase becomes discontinuous, and for dry soils the water phase does, the physics of these phase transitions represents potential trouble for numerical modeling. But to put the demands of the numerical modeling first is what I would call "upside down" science.
NG31A-0852 0800h
Towards a High Resolution Cellular Model for Coastal Simulation (CEMCOS)
The aim of this research is to develop a cellular model for coastal simulation in response to changing climate and sea-level, as a contribution to the UK Tyndall Centre's Research Theme 4: Sustaining the Coastal Zone. The modelling approach uses simple cell-based rules of sediment erosion, transport and deposition operating between adjacent cells. This enables the model to include the full range of processes and properties of the coastal environment, including nonlinear behaviour, using only local interactions at discrete time intervals. Tide propagation and wave action drive sediment transport, which is further conditioned by erosion thresholds related to grain size and vegetation growth. Here, we report an overview of this one-year project and details on model design and validation. This includes tide and wave parameterisation, resulting in sediment transport over a 3-D grid of cells representing estuary morphology and bathymetry. The model (CEMCOS) is being designed to be fully generic and exportable to different coastal areas, with initial testing and validation being conducted using published bathymetric and cartographic data over the last c.150 years for the Blackwater Estuary in eastern England.
NG31A-0853 0800h
Modeling of Microbial Motion in a Fractal Porous Media
The evolution of genetic information between disparate species of microbes can play an important role in many environmental and medical problems. Efforts to model this phenomenon on scales ranging from the micron to the field are underway. One aspect of this work has been the development of an upscaled equation for a microbe swimming in a fractal porous media, where the fractal dimension at the various scales is computed. CLT's for heavy tailed sticky stochastic processes are employed in this process. Current results on the modeling effort will be presented.
NG31A-0854 0800h
A damage-mechanics model for crustal deformation
The deformation of the brittle upper crust is primarily associated with displacements on faults. Nevertheless, it has often been found that continuum fluid models, usually based on a non-Newtonian viscosity, are applicable. We derive a continuum rheology for crustal deformation using damage mechanics. It is hypothesized that when a constant strain rate $\dot{\epsilon}$ is applied to a solid material the stress {\it $\sigma$} and damage increase until failure occurs, which is analogous to an earthquake. We further assume that this process is repeated, in analogy to the repetitive occurrence of earthquakes on a fault. Our model assumes that the crust behaves elastically below a yield stress {\it $\sigma$$_{y}$}. Above this stress the continuum deformations can be modeled as a non-Newtonian viscous flow with $\dot{\epsilon}$ $\sim$ ({\it $\sigma$}-{\it $\sigma$$_{y}$})$^{{\it n}}$ where {\it n} is constant. We derive the modified Omori's law for aftershock decay using a viscoelastic version of our model and get good agreement with observations taking {\it n} = 6. Using parameter values appropriate for aftershocks, we obtain a continuum crustal rheology that can explain major orogenies such as the Indian-Asian collision.
NG31A-0855 0800h
Study of Low-Frequency Earth motions from Earthquakes and a Hurricane using a Modified Standard Seismometer
The modification of a WWSSN Sprengnether vertical seismometer has resulted in significantly improved performance at low frequencies. Instead of being used as a velocity detector as originally designed, the Faraday subsystem is made to function as an actuator to provide a type of force feedback. Added to the instrument to detect ground motions is an array form of the author's symmetric differential capacitive (SDC) sensor. The feedback circuit is not conventional, but rather is used to eliminate long-term drift by placing between sensor and actuator an operational amplifier integrator having a time constant of several thousand seconds. Signal to noise ratio at low frequencies is increased, since the modified instrument does not suffer from the 20dB/decade falloff in sensitivity that characterizes conventional force-feedback seismometers. A Hanning-windowed FFT algorithm is employed in the analysis of recorded earthquakes, including that of the very large Indonesia earthquake (M 7.9) of 25 July 2004. The improved low frequency response allows the study of the free oscillations of the Earth that accompany large earthquakes. Data will be provided showing oscillations with spectral components in the vicinity of 1 mHz, that frequently have been observed with this instrument to occur both before as well as after an earthquake. Additionally, microseisms and other interesting data will be shown from records collected by the instrument as Hurricane Charley moved across Florida and up the eastern seaboard.
http://physics.mercer.edu/hpage/peters.html
NG31A-0856 0800h
Measuring the Complexity of Seismicity Pattern Evolution
``Complexity'' has become an ubiquitous term in science. However, there is, much as with ``fractality'', no clear definition of what complexity actually means. Yet, it is important to distinguish between what is merely complicated and what is complex in the sense that simple rules can give rise to very rich behaviour. Seismicity is certainly a complicated phenomenon (difficult to understand) but simple models such as cellular automata indicate that earthquakes are truly complex. From the observational point of view, there exists the problem of quantification of complexity in real world seismicity patterns (in the absence of even a rigid definition of complexity). Such a measurement is desirable, however, not only for fundamental understanding but also for monitoring and possibly for prediction purposes. Maybe the most workable definitions of complexity exist in informatics, summarised under the topic of algorithmic complexity. Here, after introducing the concepts, I apply such measures of complexity to temporally evolving seismicity patterns from different geographic regions. Finally, I discuss the usefulness of the approach and discuss results in view of the occurrence of large earthquakes.
NG31A-0857 0800h
Hierarchical Description of Evolution of an Inverse Cascade in Percolation Model
The dynamics of a 2D site percolation model on a square lattice is studied using the hierarchical approach introduced by Gabrielov, Newman, and Turcotte [{\it Phys. Rev. E}, {\bf 60}, 5293-5300, 1999]. The central role in this approach is played by the Horton-Strahler rule for ranking elements within a hierarchical structure. In percolation model a hierarchy is created by the temporal evolution of the system that allows one to represent an inverse cascade of particle aggregation as a time-oriented tree. Our main results are the following: A) The time-dependent scaling laws for cluster ranks are derived using the Tokunaga branching constraint and the classical results on percolation in terms of cluster masses. Remarkably, at percolation these laws coincide with the corresponding laws obtained by Gabrielov, Newman, and Turcotte [{\it Phys. Rev. E}, {\bf 60}, 5293-5300, 1999] in a steady-state approximation to a general aggregation process. B) The three-exponent time-dependent scaling for the cluster rank distribution is reported in deviation from the two-exponent scaling well-known for the mass distribution. C) Deviations from the pure scaling at percolation and their time-dependent evolution are described. In addition, an empirical constraint on the dynamics of a rank population is reported based on extensive numerical simulations.
NG31A-0858 0800h
Flexure with Damage
Investigations in structural geology and geophysics often apply continuum mechanics to solve problems relating to the deformation of the crust and lithosphere, such as the bending of strata due to a laccolith, bending of the lithosphere under island chains, bending of the lithosphere at an ocean trench. These solutions are largely based on linear elasticity. However, many processes involve stresses that exceed the elastic limit. Thus plastic, as well as elastic, deformation occurs. The temporal and spatial changes in material rheology and the nonlinear nature of the process preclude the development of analytical solutions in these complex cases. To account for the evolving rheology, we apply continuum damage mechanics as an empirical method to solve the problem of a bending beam. We use a numerical method to obtain quasi-static solutions to the Navier equation. We use the program GeoFEST v 4.5 (Geophysical Finite Element Simulation Tool), developed by NASA Jet Propulsion Laboratory, to generate solutions for each time step. Where the Von Mises stresses exceed the critical stress, we apply damage to the elements and reduce the shear modulus of the element. Damage is calculated for each time step by a power law relationship of the ratio of the critical stress to the Von Mises stress and the critical strain to the Von Mises strain, accounting for relaxation of the material due to increasing damage. To test our method, we apply damage rheology to a 2-D simple beam deforming under its own weight. This problem can be considered an analog for folding. Where stresses exceed the critical stress, we simulate the formation of damage and observe the time-dependent relaxation of the stress and strain to levels below the plastic limit. Thus damage can be used as a proxy for irreversible deformation in the fold hinge area, representing brittle fracture and microcracking where extensional fiber stresses dominate, and material dissolution where compressional fiber stresses dominate.
NG31A-0859 0800h
Using the Hilbert-Huang Transform to Improve Seismic Profiling of Gas Hydrates in the Gulf of Mexico
Advancements in the collection and processing of seismic reflection data allow for improved imaging and analysis of complex targets. High resolution (10,000+ samples/sec) marine vertical cable (VC) data from the Atwater Valley (AT14) block in the Gulf of Mexico are analyzed for gas hydrate content. The gas hydrates in this region form in thick, Pleistocene sediments and lack the presence of a Bottom Simulating Reflector (BSR) on previously recorded multi-channel seismic reflection data at selected sites. The goals of this research are to: 1) assess the ability of the Hilbert-Huang transform (HHT) to quantify meaningful geologic information in both the time and frequency domains regarding these anomalous gas hydrates, and 2) develop a processing flow employing the HHT to prepare the data for velocity analysis. The advantage of the HHT over Fourier methods is freedom from the criterion that the analyzed signal must be stationary and linear. Most acoustic waves returning from the subsurface are both nonlinear and non-stationary and, therefore, Fourier techniques may fall short of providing the best possible analysis. Further, the HHT allows for empirically derived characteristics to be used in filter design and application, resulting in better filter performance and enhanced signal-to-noise ratio over other techniques.
NG31A-0860 0800h
A Microstructural Study of Small-Displacement Faults in Aztec Sandstone
Previous studies indicate that brittle shear localization microstructures develop during the initial increments of shear displacement. We studied gouge samples from faults in Aztec quartz sandstone (Valley of Fire State park, Nevada) with shear displacements in the order of 10-1500mm. Undeformed Aztec sandstone near the sampling site had well-rounded grains with average size of 550$\mu$m and typical porosity of 23$%$. The total gouge zone thickness, measured parallel with slickenside lineation/perpendicular to shear plane ranged from 1-47mm. Average shear strain $\gamma$ in the samples, calculated as the ratio of shear displacement (true displacement) to average zone thickness measured over 1m length of fault, ranged from 14 to 100. Sections of the gouge were imaged under SEM in backscattered mode at 250, 500, and 1000 times magnifications. Individual particle outlines on images from each sample were manually traced on digital overlays, which were reproduced as binary images and used in microstructural measurements. Particle shapes were measured by a new shape descriptor algorithm POL (particle outline linearity), which returned POL values in N straight sides per particle (Ns/P). In the undeformed Aztec Ns/P$\sim$0. We combined data from all magnifications to reduce measurement errors due to large particle size variability of the gouge. The gouge microstructures became more complex with increasing shear strain (rather than shear displacement). Y-shears were absent at $\gamma$14, but began to appear in the gouge at $\gamma$26. However, incipient damage zones at the lowest shear strain contained clear sets of R shears. Multiple Y shear surfaces and damage zones containing R-shears are observed at $\gamma$31. Microstructures suggestive of multiple R and Y shear surfaces were observed at $\gamma$97 and $\gamma$100. In all cases, Y shear surfaces appeared as surrounded by zones of high comminution that varied in thickness as much as an order of magnitude along the sample length. Median size of particles in the core region determined on PSD curves was reduced from 9$\mu$m ($\gamma$14) to 3 $\mu$m ($\gamma$97). In contrast, particle size reduction in the damage zone was minimal compared to the average undeformed particle size. POL values for the core region dropped from 1.5s/P at $\gamma$14 to 0.6s/P at $\gamma$97. The fractal dimension values (slope of the log-log cumulative PSD) for the core region changed from 2 to 2.3 with increasing $\gamma$. The particle shape profiles across the gouge zone reach maximum in the damage zone region then approach the undeformed Ns/P values for the core region. The form of the profiles remains more or less unchanged for all samples in terms of the maximum value for the danage zone. The particle shape and size evolution with increased $\gamma$ indicates that most comminution occurs in the core region, leaving the damage zone mostly inactive at $\gamma$$>$20. Our results suggest that the damage zone/core structure in Aztec faults developed at $\gamma$30-$\gamma$50. Reported results for experimental faults with quartz gouge sheared at 25-75MPa pressures suggest that the Aztec faults were deformed under lower normal stresses.
NG31A-0861 0800h
Deformation Heterogeneity Within an Accretionary Prism and its Instability Through Time; Insights From Sandbox Experiments and Particle Simulations
The formation of accretionary prisms at subduction margins can be modelled and examined by using analogue experiments and numerical simulations. We have conducted sandbox experiments and distinct element simulations, both of which approximate the geologic body as an assembly of particles. Such granular materials can appropriately model the brittle deformation of the upper crust thus have been widely used to examine fault-related structures. During the accretion process, the velocity and stress vectors are highly heterogeneous and unstable in the both experiments and simulations. Due to the brittle approximation of the models, the deformation can be characterised by frictional faulting. Such frictional faulting is generally controlled by a series of intermittent displacement, so-called O^stick-slipO motions. Since the stick-slip motions occur due to accumulation/release cycles of elastic energy along fault surfaces, the stress field should also be cyclically distorted. Provided that many faults in a prism, the stress field would presumably be affected by such distortion caused by each faulting event. The instability in the particle velocity and stresses would therefore due to the stick-slip behaviour of the faults. The velocity and stress variations in an actual accretionary prism are poorly investigated. The models shown in this paper can be applied to understand such natural instability in the geo-environment and this technique might be used as a prediction tool of geo-hazards in a near future.
NG31A-0862 0800h
Aftershocks In Massless Cellular Automaton Slider-Block Models.
We present preliminary results for a modified Rundle-Jackson-Brown model that generates clusters of aftershocks. The model is represented by the two-dimensional array of massless blocks connected by springs to its neighbors and the loader plate. Stress is introduced to the system by moving the loader plate with infinitesimally low velocity and stress is dissipated by the toppling sites. The residual value of the toppled site is a random variable with prescribed noise amplitude. We study the system with different ranges of interaction. Our goal is to observe Omori-type laws for aftershocks under the condition that statistics of all events still obey the Gutenberg-Richter law. In addition, we are looking for aftershock time sequences that are not induced by the loader plate motion; that is, they are present in the model for a non-moving loader plate. We also observe that, for systems with a large range of interaction (called near mean-field systems), the frequency-size statistics exponent changes from the expected 1.5 to a somewhat larger value. The distribution of inter event times is also studied and shown to obey a power-law decay.
NG31A-0863 0800h
Preparation for Mainshocks: a Closer Look at Correlation Evolution
The critical point hypothesis of seismicity proposes that the preparation for large earthquakes involves the progressive formation of long-range spatial correlations in the regional stress field. Smaller earthquakes in the surrounding region are responsible for this correlation evolution. The observable signature of correlation evolution is accelerating seismic energy release, a phenomenon that has been observed in a number of tectonic regions. Accelerating energy release has been observed in earthquake simulations with evidence for correlation evolution obtained by examining the evolution of the two point spatial correlation function of the stress field. These previous studies did not closely examine the correlation evolution within the region affected by the mainshock but rather examined the correlation evolution of the entire modelled region. In cases where mainshocks only affect a fraction of the modelled region, it is difficult to detect correlation evolution. In the current investigation, we re-examine correlation evolution within cellular automaton models of earthquake fault systems. We focus upon stress field evolution only within the region containing sites that fail in a subsequent mainshock. In addition, we track the spatial extent of precursors that alter the stress within the mainshock failure region. This provides a measure of the critical region size for accelerating energy release. We compare power-law fits to cumulative energy release within the critical regions with power-law fits to cumulative energy release within the entire modelled region. Preliminary results indicate there is a systematic reduction in short-range correlations as a mainshock approaches, accompanied by formation of long-range correlations for distances approximately twice the effective interaction range of the model.
NG31A-0864 0800h
Stochastic Resonance In The Rikitake Dynamo: An Implication For The Relationship Between Geomagnetic Reversal And Glacial Events
Not yet a theoretical analysis can explain the coincident temporal correlation between the geomagnetic reversal and glacial events, which both have a quasi-period of about 100 kyr, although there exists dozens of observational evidences for such correlation. In this work, by simulating the behavior of a simple Rikitake dynamo subject to an external periodic force, we show a series of quasi-periodic polarity reversals can be embedded in the geomagnetic filed via the mechanism of stochastic resonance. The term of "stochastic resonance" describes the group of effects in nonlinear system, whereby the response of the system to the weak external, periodic signal is remarkably amplified by the increase of noise intensity. We consequently suggest a common triggering mechanism for the geomagnetic reversal and glacial events, neither the glacial epoch controls the geomagnetic epoch nor vice versa. Instead, both kinds of catastrophes may result from the cyclic variation of the Earth's orbital eccentricity. Our demonstration of stochastic resonance in the Rikitake dynamo thus provides the first theoretical evidence for the relationship between two kinds of catastrophes, the geomagnetic reversal and glacial events, in the Earth's history.
NG31A-0865 0800h
Thermal Gradients Effects on Slow Dynamics in Geomaterials
In recent years several anomalous elastic phenomena have been seen in different materials as rocks, sandstones. Perhaps one of the most interest and unsolved feature is the so-called slow dynamics. Slow dynamics has been seen in resonance bar experiments and consists of a time-dependent recovery of an elastic modulus to its initial value after being softened by large strain. Based on the observation of intermediate-time relaxation for individual cracks in a solid, it has been suggested recently that slow decrease of temperature gradients can account for the observed long-time behavior in resonant bar experiments for both cracked and undamaged materials. Here we critically examine this proposal and discuss several possible implementations (based on differing assumptions and simplifications).
NG31A-0866 0800h
Neutron Diffraction Study of the Contribution of Grain Contacts to Nonlinear Stress-Strain Behavior
Repeatable, hysteretic loops in quasi-static loading measurements on rocks are well known; the fundamental processes responsible for them are not. The grain contact region is usually treated as the site of these processes, but there is little supporting experimental evidence. We have performed simultaneous neutron diffraction and quasi-static loading experiments on a selection of rocks to experimentally isolate the response of these contact regions. Neutron diffraction measures strain in the lattice planes of the bulk of the grain material, so differences between this strain and the macroscopic response yield information about grain contact behavior. We find the lattice responds linearly to stress in all cases, oblivious to the macroscopic unrecoverable strains, curvature, and hysteresis, localizing these effects to the contacts. Neutron diffraction shows that the more granular rocks appear to distribute stresses so that the same strain appears in all the grains, independent of crystallographic orientation. [Work supported by Los Alamos Institutional Support (LDRD) and the DOE Office of Basic Energy Sciences. The Manuel Lujan Jr. Neutron Scattering Center is a national user facility funded in part by the U.S. DOE.]
NG31A-0867 0800h
A Cooperative Test of the Load/Unload Response Ratio Proposed Method of Earthquake Prediction
The Load/Unload Response Ratio (LURR) method is a proposed technique to predict earthquakes that was first put forward by Yin in 1984 (Yin, 1987). LURR is based on the idea that when a region is near failure, there is an increase in the rate of seismic activity during loading of the tidal cycle relative to the rate of seismic activity during unloading of the tidal cycle. Typically the numerator of the LURR ratio is the number, or the sum of some measure of the size (e.g. Benioff strain), of small earthquakes that occur during loading of the tidal cycle, whereas the denominator is the same as the numerator except it is calculated during unloading. LURR method suggests this ratio should increase in the months to year preceding a large earthquake. Regions near failure have tectonic stresses nearly high enough for a large earthquake to occur, thus it seems more likely that smaller earthquakes in the region would be triggered when the tidal stresses add to the tectonic ones. However, until recently even the most careful studies suggested that the effect of tidal stresses on earthquake occurrence is very small and difficult to detect. New studies have shown that there is a tidal triggering effect on shallow thrust faults in areas with strong tides from ocean loading (Tanaka et al., 2002; Cochran et al., 2004). We have been conducting an independent test of the LURR method, since there would be important scientific and social implications if the LURR method were proven to be a robust method of earthquake prediction. Smith and Sammis (2003) also undertook a similar study. Following both the parameters of Yin et al. (2000) and the somewhat different ones of Smith and Sammis (2003), we have repeated calculations of LURR for the Northridge and Loma Prieta earthquakes in California. Though we have followed both sets of parameters closely, we have been unable to reproduce either set of results. A general agreement was made at the recent ACES Workshop in China between research groups studying LURR to work cooperatively to discover what is causing these differences in results. All parties will share codes and data sets, be more specific regarding the calculation parameters, and develop a synthetic data set for which we know the expected LURR value. Each research group will then test their codes and the codes of other groups on this synthetic data set. The goal of this cooperative effort is to resolve the differences in methods and results and permit more definitive conclusions on the potential usefulness of LURR in earthquake prediction.
NG31A-0868 0800h
On-off intermittency in earthquakes occurrence
The intermittent behaviour is characterized by no sharp transition from an equilibrium quiescent state (laminar phase) to an active state(burst). When the mechanism of transition is driven by some control parameters, the intermittency is called on-off intermittency. This is characterized by some universal statistical properties. Here we show that the occurrence of earthquake clusters could be viewed as the bursts of activity of an on-off intermittent phenomenon. This interpretation is unfortunately not universal in the case of earthquakes because it depends by the choice of a rate of occurrence threshold. The value of this threshold could influence the transition to a chaotic behaviour.
NG31A-0869 0800h
An Earthquake Prediction System Using The Time Series Analyses of Earthquake Property And Crust Motion
An earthquake (EQ) phenomenon has evidence of deterministic chaos. A total of about 17200 EQ's with magnitude M $>$= 4 are collected from a catalogue of Japan Meteorological Agency from 1983 to June of 2004 for a region of (24 deg - 48 deg N, 124 deg - 150 deg E). Sequencing the five EQ properties of every EQ, which are latitude (LA), longitude (LN), depth (DP), inter-EQ time interval (IT) and M, in EQ occurrence (event) order, we find that each of the five EQ property series is deterministic chaos.[1,2] For example, the largest Lyapunov exponents are all positive values, statistically distinct from those of the series surrogated by randomly shuffling the event order. Each property series in chronological event order i, is given by Da = [Da,1, Da,2, . , Da,i-1, Da,i, Da,i+1, .]. (1) Here index a stands for each property (a = LT, LN, DP, IT and M). Each minimum embedding dimension (ED) of Eq. 1 is only five (which happens to be our five EQ properties). It is estimated by finding the ED at which the percentage of false nearest neighbors drops to a constant residual level. The residue is indicative of the contamination level of dynamical noise created by many other seismogenic variables. To reduce the residue of each series to zero, we take the moving average (denoted by Da,m,w) of each property element of Eq. 1 over w consecutive events with respect to event i running from m - w + 1 to m. To extract the rate of change in Da,m,w, we use the second order difference at an event-separation s, defined as Aa,m,w,s = (Da,m-2s,w - 2 Da,m-s,w + Da,m,w). To extract the determinism in seismogenic evolutions (quiescence cycles) to only large EQ's, we use the moving sum (CI-w) of element Da,i (a=IT) over w consecutive events from m - w + 1 to m. With an appropriate choice of w (for example, w = 100), CI-w reveals the deterministic measures that are absent in its surrogate. Thus the analysis of deterministic Da,m,w, Aa,m,w,s and CI-w should enable us to predict the time, focus and M of a large EQ within narrow limits in weeks or months (or a few years) ahead of time. We have developed such a short-term deterministic EQ forecasting system similar to those used for Typhoons and Hurricanes, which has been under a test operation at http://www.tec21.jp/ since June of 2003. [1,2] The system must divide Japan into a small area of about 5 deg by 5 deg for which Eq. 1 is reconstructed such that the regional CI-w and Aa,m,w,s (whose ED's are all reduced to three) become the deterministic measures to make the successful prediction tests on every large EQ (or swarm if any) of hindsight in the area. The current system has five areas to cover Japan. We focus on two examples to describe the system operation. One is the 2003/09/26 Tokachi EQ of M 8 in hindsight (the system was yet to cover this area at the event). To make a prediction test on the M 8 EQ, we assume our current date is back to 2003/08/31. The date prediction of the M 8-class EQ was only one day off. The focus prediction was within the very narrow limits. Another is a successful rollout of the most recent forecast on the 2004/05/30 EQ of M 6.7 off coast of the southern Kanto (Tokyo) area. Its forecasting at our website started 16 days ahead of time like forecasting an approaching typhoon. The final forecast issued one day before the actual event has confirmed a perfect prediction on the focus and date. The system also performs a state-space analysis of the daily crust motion observed by GPS (F1 data of GEONET) to detect any anomaly including a slow-slip motion precursory to the M 8 EQ. 1. F. Takeda, and M. Takeo, submitted to Chaos (2003). 2. F. Takeda, and M. Takeo, submitted to AIP Conf. Proc., ECC8 (2004).
http://www.tec21.jp