Rate Of Seismic Release Research Articles

A Complexity View into the Physics of the Accelerating Seismic Release Hypothesis: Theoretical Principles.

Observational indications support the hypothesis that many large earthquakes are preceded by accelerating-decelerating seismic release rates which are described by a power law time to failure relation. In the present work, a unified theoretical framework is discussed based on the ideas of non-extensive statistical physics along with fundamental principles of physics such as the energy conservation in a faulted crustal volume undergoing stress loading. We define a generalized Benioff strain function , where Ei is the earthquake energy, . and a time-to-failure power-law of derived for a fault system that obeys a hierarchical distribution law extracted from Tsallis entropy. In the time-to-failure power-law followed by the existence of a common exponent mξ which is a function of the non-extensive entropic parameter q is demonstrated. An analytic expression that connects mξ with the Tsallis entropic parameter q and the b value of Gutenberg—Richter law is derived. In addition the range of q and b values that could drive the system into an accelerating stage and to failure is discussed, along with precursory variations of mξ resulting from the precursory b-value anomaly. Finally our calculations based on Tsallis entropy and the energy conservation give a new view on the empirical laws derived in the literature, the associated average generalized Benioff strain rate during accelerating period with the background rate and connecting model parameters with the expected magnitude of the main shock.

Critical-point behaviour in self-organizing systems: the September 1999 Athens earthquake and Stock Market correction

A quorum of observational and theoretical evidence indicates that seismogenesis is a critical phenomenon culminating with a large event that corresponds to some critical point: large earthquakes are preceded by the self-organization of the fault network and power-law acceleration of the seismic release rates. The stock market is not very different: the (interaction of the traders is usually irreversible and determines the value of the stock, which determines the actions of other traders etc. Thus, the stock market becomes a self-organizing system and exhibits strong analogies with other self-organizing systems, such as earthquakes. Positive feed-back is also important and may lead to trend-chasing and rapid escalation of stock price. There is ample evidence that market crashes and large corrections are often preceded by speculative bubbles with power law acceleration of the market price. In diabolic coincidence, both such crises were observed in Athens during the September of 1999. On 7/9 a moderate (M5.9) but destructive earthquake; around 22/9 the Athens Stock Exchange rally of the past few months crashed. Both phenomena were preceded by characteristic power-law acceleration, respectively in crustal deformation and market growth. Two very different complex dynamic systems are shown to exhibit similar collective behaviour, pointing out the apparent universality of natural order.

On the nature and dynamics of the seismogenetic systems of North California, USA: An analysis based on Non-Extensive Statistical Physics

We examine the nature of the seismogenetic system in North California, USA, by searching for evidence of complexity and non-extensivity in the earthquake record. We attempt to determine whether earthquakes are generated by a self-excited Poisson process, in which case they obey Boltzmann-Gibbs thermodynamics, or by a Critical process, in which long-range interactions in non-equilibrium states are expected (correlation) and the thermodynamics deviate from the Boltzmann-Gibbs formalism. Emphasis is given to background seismicity since it is generally agreed that aftershock sequences comprise correlated sets. We use the complete and homogeneous earthquake catalogue published by the North California Earthquake Data Centre, in which aftershocks are either included, or have been removed by a stochastic declustering procedure. We examine multivariate cumulative frequency distributions of earthquake magnitudes, interevent time and interevent distance in the context of Non-Extensive Statistical Physics, which is a generalization of extensive Boltzmann-Gibbs thermodynamics to non-equilibrating (non-extensive) systems. Our results indicate that the seismogenetic systems of North California are generally sub-extensive complex and non-Poissonian. The background seismicity exhibits long-range interaction as evidenced by the overall increase of correlation observed by declustering the earthquake catalogues, as well as by the high correlation observed for earthquakes separated by long interevent distances. It is also important to emphasize that two subsystems with rather different properties appear to exist. The correlation observed along the Sierra Nevada Range – Walker Lane is quasi-stationary and indicates a Self-Organized Critical fault system. Conversely, the north segment of the San Andreas Fault exhibits changes in the level of correlation with reference to the large Loma Prieta event of 1989 and thus has attributes of Critical Point behaviour albeit without acceleration of seismic release rates. SOC appears to be a likely explanation of complexity mechanisms but since there are other ways by which complexity may emerge, additional work is required before assertive conclusions can be drawn.

A first principles approach to understand the physics of precursory accelerating seismicity

Observational studies from rock fractures to earthquakes indicate that fractures and many large earthquakes are preceded by accelerating seismic release rates (accelerated seismic deformation). This is characterized by cumulative Benioff strain that follows a power law time-to-failure relation of the form C(t) = K + A(Tf – t)m, where Tf is the failure time of the large event, and m is of the order of 0.2-0.4. More recent theoretical studies have been related to the behavior of seismicity prior to large earthquakes, to the excitation in proximity of a spinodal instability. These have show that the power-law activation associated with the spinodal instability is essentially identical to the power-law acceleration of Benioff strain observed prior to earthquakes with m = 0.25-0.3. In the present study, we provide an estimate of the generic local distribution of cracks, following the Wackentrapp-Hergarten-Neugebauer model for mode I propagation and concentration of microcracks in brittle solids due to remote stress. This is a coupled system that combines the equilibrium equation for the stress tensor with an evolution equation for the crack density integral. This inverse type result is obtained through the equilibrium equations for a solid body. We test models for the local distribution of cracks, with estimation of the stress tensor in terms of the crack density integral, through the Nash-Moser iterative method. Here, via the evolution equation, these estimates imply that the crack density integral grows according to a (Tf – t)0.3-law, in agreement with observations.

A decade of passive seismic monitoring experiments with local networks in four Italian regions

We report on four seismic monitoring experiments that in the past ten years we carried out with dense local networks in seismically active Italian areas where for at least a year, tens of three component seismic stations were set up to record microseismicity. The areas observed are Alpago–Cansiglio, located in the Venetian Alps, Città di Castello in the Northern Apennines, Marsica in the Central Apennines and Val d'Agri located in the Southern Apennines. We produced homogeneous catalogues regarding earthquake locations and local magnitudes to investigate seismicity patterns during an inter-seismic period. The four regions are characterised by different kinematics, strain rates and historical/recent seismicity. We investigate earthquake distribution in space, time and size obtaining reference seismic rates and parameters of the Gutenberg and Richter law. We declustered the catalogues to look for coherent signs in the background seismic activity. Despite a difference in the catalogues magnitudes of completeness due both to the diverse detection threshold of the local networks and different seismic release, we detect and observe two common main behaviours: a) The Alpago–Cansiglio and Marsica regions are characterised by a relatively lower rate of seismic release associated to the episodic occurrence of seismic sequences with the largest event being 3 < M L < 4. In these areas the seismicity is not localised around the main faults. b) The Città di Castello and Val d'Agri regions have a relatively high rate of seismicity release almost continuously with time, and the increase in earthquake production is not clearly related to seismic sequences. In these areas the seismicity nucleates around defined fault systems and is usually lower than M L < 3. We suggest that the presence of over-pressured fluids in the Città di Castello and Val d'Agri uppermost crustal volume may favour and mould the higher rate of microseismic release.

Distributed power-law seismicity changes and crustal deformation in the SW Hellenic ARC

Abstract. A region of definite accelerating seismic release rates has been identified at the SW Hellenic Arc and Trench system, of Peloponnesus, and to the south-west of the island of Kythera (Greece). The identification was made after detailed, parametric time-to-failure modelling on a 0.1° square grid over the area 20° E – 27° E and 34° N–38° N. The observations are strongly suggestive of terminal-stage critical point behaviour (critical exponent of the order of 0.25), leading to a large earthquake with magnitude 7.1 ± 0.4, to occur at time 2003.6 ± 0.6. In addition to the region of accelerating seismic release rates, an adjacent region of decelerating seismicity was also observed. The acceleration/deceleration pattern appears in such a well structured and organised manner, which is strongly suggestive of a causal relationship. An explanation may be that the observed characteristics of distributed power-law seismicity changes may be produced by stress transfer from a fault, to a region already subjected to stress inhomogeneities, i.e. a region defined by the stress field required to rupture a fault with a specified size, orientation and rake. Around a fault that is going to rupture, there are bright spots (regions of increasing stress) and stress shadows (regions relaxing stress); whereas acceleration may be observed in bright spots, deceleration may be expected in the shadows. We concluded that the observed seismic release patterns can possibly be explained with a family of NE-SW oriented, left-lateral, strike-slip to oblique-slip faults, located to the SW of Kythera and Antikythera and capable of producing earthquakes with magnitudes MS ~ 7. Time-to-failure modelling and empirical analysis of earthquakes in the stress bright spots yield a critical exponent of the order 0.25 as expected from theory, and a predicted magnitude and critical time perfectly consistent with the figures given above. Although we have determined an approximate location, time and magnitude, it is as yet difficult to assert a prediction for reasons discussed in the text. However, our results, as well as similar independent observations by another research team, indicate that a strong earthquake may occur at the SW Hellenic Arc, in the next few years.

Did the 7/9/1999 M5.9 Athens Earthquake Come with a Warning?

Prior to the 7/9/1999 MS = 5.9 Athens earthquake, regional seismicity has exhibited a power-law increase, of the form �� = K +A(tc −t) n ,w hereis estimated using an expression log � = cM + d and tc is the time of the culminating event. Such changes appeared after the 17/8/1999 M7.4 Izmit event. We quantified the performance of the power law vs. the null hypothesis of constant seismic release rates, by defining the curvature C as the ratio of the power law fit RMS/linear fit RMS, so that the smaller C is, the better the power law behaviour. By mapping C, we have established a critical radius of 110 km and observed that the region of correlated accelerating seismic release extended from the N. Aegean, through Euboea and Attica to the SW Peloponnese. A few days prior to the Athens event, min(C) was centred at the epicentral area and numerical simulation yielded tc = 1999.676 and predicted MS = 5.77. Seismicity rates returned to normal (quasi-constant) after the Athens event. We interpret this effect as critical point behaviour, following remote excitation of a broad area by stress redistribution due to the Izmit event which, at Athens, has triggered 'premature' failure of a fault nearing its load bearing capacity. If this is correct, we have documented a case of remote earthquake triggering by another earthquake, as well as insight into the mechanisms produ- cing it. As a corollary, we note that a large event may beget another large event in its broader region of interaction, which may be preceded by characteristic precursory seismicity changes.

Crustal strain in central Greece from repeated GPS measurements in the interval 1989-1997

A 66-station GPS network spanning central Greece, first observed in 1989, has been occupied fully on three occasions: June 1989, October 1991 and May 1993. Subsets of this network bounding the Gulf of Korinthos have also been occupied in June 1995, October 1995, May 1996 and September/October 1997. The first three occupations were processed using a fiducial GPS methodology, whereas later surveys were processed using CODE precise orbits. Combination of data from different surveys to yield smooth site velocities requires global network translations at each epoch to compensate for errors in the realization of the reference frame. This method provides a posteriori estimates of the relative coordinate errors and reference frame noise. Only one earthquake, the 1995 June 15 Egion event, has caused significant local coseismic displacement, and its effects on the interseismic velocity field are removed using an elastic dislocation model. We constrain the orientation of the 100 yr triangulation—GPS velocity estimates of Davies et al. (1997) using 14 sites common to the two networks. The goodness of fit of this transformation indicates that the short-term and 100 yr geodetic estimates of deformation are highly compatible. We infer that short-term geodetic studies are capable of determining longer-term deformation rates provided that transient, local effects can be modelled. From the combined velocity field, we estimate principal strains and rigid-body rotation rates at points on a regular grid using data from neighbouring sites. Strain rates are high within the Gulf of Korinthos and much lower elsewhere. The extension rate across the Gulf of Korinthos increases from east to west. Comparison of the extension rate with historical and recent rates of seismic release of strain reveals significant medium-term seismic hazard in the western Gulf of Korinthos, and may also indicate long-term aseismic strain.

On the cessation of seismicity at the base of the transition zone

Through a detailed analysis of seismicity at the base of the transition zone, we obtain an updated value of the maximum reliable depth of confirmed seismicity, we investigate regional variation in the maximum depth of seismicity among those Wadati-Benioff zones which reach the bottom of the transition zone, and we attempt to quantify the maximum possible rate of seismic release in the lower mantle compatible with the failure to detect even a single event since the advent of modern seismological networks. We classify deep subduction zones into three groups: those whose seismicity does not reach beyond 620 km, those whose seismicity appears to terminate around 650–660 km, and Tonga-Kermadec (and the ‘Vityaz’ cluster) whose seismicity extends to 685–690 km. We suggest that the depth extent of seismicity is controlled by the depth of the γ → pv + mw transition responsible for the ‘660-km’ seismic discontinuity, which is deflected to greater depths in cold slabs than in warmer ones. We note that this transition marks the depth below which thermal perturbation of phase transitions no longer generates buoyancy anomalies and their large attendant down-dip compressive stresses and below which strain energy generated by other mechanisms may not accumulate to seismogenic levels due to superplastic weakness in fine-grained materials. We find that the maximum level of seismic activity in the lower mantle must be at least three orders of magnitude less than that observed in the transition zone.

Predictive modeling of the seismic cycle of the Greater San Francisco Bay Region

The seismic cycle for the San Francisco Bay region is synthesized by a model combining the pre‐and post‐1906 seismic histories. The long‐term acceleration of seismic release (seismic moment, Benioff strain release, or event count) in the seismic cycle and the shorter‐term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique, called time‐to‐failure analysis, in which rate of seismic release is proportional to an inverse power of the remaining time to failure. The exponent of time to failure in the accelerating sequences appears to be scale invariant, and the length of the full cycle is estimated at 269 ± 50 years. The 1989 Loma Prieta earthquake, which is the culmination of the first subcycle in the present long‐term seismic cycle, should have been predictable with an uncertainty of 2 years in time and 0.5 in magnitude, although the specific location (at Loma Prieta) was not predictable by this technique. If our model is correct and if the Loma Prieta earthquake is the culmination of a subcycle, the San Francisco Bay region should be entering a relatively long (20–50 years) period of seismic quiescence above magnitude 6. A great earthquake, such as the 1906 San Francisco event, would appear to be more than a century in the future.