Correlation length as an indicator of critical point behavior prior to a large earthquake (original) (raw)
Related papers
Journal of Geophysical Research: Solid Earth, 2001
We test the critical point concept for earthquakes in terms of the spatial correlation length. A system near a critical point is associated with a diverging correlation length following a power law time-to-failure relation. We estimate the correlation length directly from an earthquake catalog using single-link cluster analysis. Therefore we assume that the distribution of moderate earthquakes re ects the state of the regional stress eld. The parameters of the analysis are determined by an optimization procedure, and the results are tested against a Poisson process with realistic distributions of epicenters, magnitudes, and aftershocks. A systematic analysis of all earthquakes with M 6:5 in California since 1952 is conducted. In fact, we observe growing correlation lengths in most cases. The null hypothesis that this behavior can be found in random data is rejected with a con dence level of more than 99%. Furthermore, we nd a scaling relation log R 0:7M (log h max i 0:5M), between the mainshock magnitude M and the critical region R (the correlation length h max i before the mainshock), which is in good agreement with theoretical values.
Correlations in aftershock and seismicity patterns
Tectonophysics, 2006
Correlations in space and time play a fundamental role in earthquake processes. One direct manifestation of the effects of correlations is the occurrence of aftershocks due to the stress transfer in the vicinity of a main shock. Less obvious and more speculative changes in correlations may occur in the background seismicity before large earthquakes. Using statistical physics it is possible to introduce a measure of spatial correlations through a correlation length. This quantity characterizes how local fluctuations can influence the occurrence of earthquakes over distances comparable with the correlation length. In this work, the physical basis of spatial correlations of earthquakes is discussed in the context of critical phenomena and the percolation problem. The method of two-point correlation function is applied to the seismicity of California. Well defined variations in time of the correlation length are found for aftershock sequences and background seismicity. The scaling properties of our obtained distributions are analyzed with respect to changes in several scaling parameters such as lower magnitude cutoff of earthquakes, the maximum time interval between earthquakes, and the spatial size of the area considered. This scaling behavior can be described in a unified manner by utilizing the multifractal fit. Utilizing the percolation approach the time evolution of clusters of earthquakes is studied with the correlation length defined in terms of the radius of gyration of clusters. This method is applied to the seismicity of California.
Increased correlation range of seismicity before large events manifested by earthquake chains
Tectonophysics, 2006
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.
Influence of Time and Space Correlations on Earthquake Magnitude
Physical Review Letters, 2008
A crucial point in the debate on feasibility of earthquake prediction is the dependence of an earthquake magnitude from past seismicity. Indeed, whilst clustering in time and space is widely accepted, much more questionable is the existence of magnitude correlations. The standard approach generally assumes that magnitudes are independent and therefore in principle unpredictable. Here we show the existence of clustering in magnitude: earthquakes occur with higher probability close in time, space and magnitude to previous events. More precisely, the next earthquake tends to have a magnitude similar but smaller than the previous one. A dynamical scaling relation between magnitude, time and space distances reproduces the complex pattern of magnitude, spatial and temporal correlations observed in experimental seismic catalogs.
The earthquake magnitude is influenced by previous seismicity
Geophysical Research Letters, 2012
Seismic occurrence is characterized by clustering in space, time 3 and magnitude. Correlations between magnitudes of subsequent events have 4 been recently attributed to catalog incompleteness. Here we investigate the 5 effect of catalog completeness on the amplitude of magnitude correlations. 6 The analysis of two California regions with different levels of catalog accu-7 racy and different lower magnitude thresholds indicate that the amplitude 8 of correlations does not depend on catalog incompleteness. Conversely, cor-9 relations are controlled by the probability that two events belong to the same 10 mainshock-aftershock sequence. Numerical simulations of the ETAS model, 11
Premonitory raise of the earthquakes' correlation range
2000
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
Influence length and space-time correlation between earthquakes
2004
Short and long range interactions between earthquakes are attracting increasing interest 1,2,3,4. Scale invariant properties of seismicity 5,6,7,8 in time, space and energy argue for the presence of complex triggering mechanisms 9 where, like a cascade process, each event produces aftershocks 10. A definitive method to assess any connection between two earthquakes separated in time and distance does not exist. Here we propose a novel method of data analysis that, based on the space-time combined generalization of the correlation integral 11 leads to a self-consistent visualization and analysis of both spatial and temporal correlations. When analyzing global seismicity we discovered a universal relation linking the spatial Influence Length of a given earthquake to the time i R τ elapsed from the event itself: , with α τ − ≈ i R 0.55 0.05 α ≅ ±. Following an event, time correlations (i.e. causality effects) exist in a region of radius that shrinks over time, suggesting a long-range dissipating stress transfer. A different process is acting in the short-range where events are randomly set, evidencing a sub-diffusive growth i R 12,13,14 of the seismogenic zone. Earthquakes appear to occur in clusters with scale invariant patterns in both space and time 7,8,15. To date, analysis has tended to focus separately on either spatial or temporal correlations, with some notable exceptions 16,17. Many earthquake properties point to a hierarchical organization, suggesting a connection among events that could be explained physically by stress transfer mechanisms and a scale invariant fracturing of the crust. Due to the complexity
Temporal correlations in the magnitude time series before major earthquakes in Japan
arXiv (Cornell University), 2016
A characteristic change of seismicity has been recently uncovered when the precursory Seismic Electric Signals activities initiate before an earthquake occurrence. In particular, the fluctuations of the order parameter of seismicity exhibit a simultaneous distinct minimum upon analyzing the seismic catalogue in a new time domain termed natural time and employing a sliding natural time window comprising a number of events that would occur in a few months. Here, we focus on the minima preceding all earthquakes of magnitude 8 (and 9) class that occurred in Japanese area from 1 January 1984 to 11 March 2011 (the day of the M9 Tohoku earthquake). By applying Detrended Fluctuation Analysis to the earthquake magnitude time series, we find that each of these minima is preceded as well as followed by characteristic changes of temporal correlations between earthquake magnitudes. In particular, we identify the following three main features. The minima are observed during periods when long range correlations have been developed, but they are preceded by a stage in which an evident anti-correlated behavior appears. After the minima, the long range correlations break down to an almost random behavior turning to anti-correlation. The minima that precede M≥7.8 earthquakes are distinguished from other minima which are either non-precursory or followed by smaller earthquakes.
On the influence of time and space correlations on the next earthquake magnitude
2007
A crucial point in the debate on feasibility of earthquake prediction is the dependence of an earthquake magnitude from past seismicity. Indeed, whilst clustering in time and space is widely accepted, much more questionable is the existence of magnitude correlations. The standard approach generally assumes that magnitudes are independent and therefore in principle unpredictable. Here we show the existence of clustering in magnitude: earthquakes occur with higher probability close in time, space and magnitude to previous events. More precisely, the next earthquake tends to have a magnitude similar but smaller than the previous one. A dynamical scaling relation between magnitude, time and space distances reproduces the complex pattern of magnitude, spatial and temporal correlations observed in experimental seismic catalogs.