Multifractal measures of synchronization of microseismic oscillations in a minute range of periods (original) (raw)
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Izvestiya, Physics of the Solid Earth, 2009
The field of low-frequency microseisms is investigated with the use of data from 83 stations of the F-net broadband network in Japan over the period from the beginning of 1997 through June 2008. Vertical components with a sampling step of 1 s are used for analysis, as well as signals with a sampling step of 1 min obtained from the initial data by averaging and thinning. Long-period regularities of changes in the singularity spectrum support width ∆α and the generalized Hurst exponent α * for the field of low-frequency microseisms were revealed by estimating multifractal singularity spectra in consecutive time windows 30 min long for 1-s data and 24 hour long for 1-min data. The average value of the parameter ∆α for 1-s data significantly decreased before the Hokkaido earthquake of September 25, 2003 ( M = 8.3), and was not restored subsequently to its previous level. Prior to September 2003, 1-min data on α * variations experienced strong annual changes, which completely ceased afterwards. Both these effects are interpreted as an increase in the degree of synchronization of microseismic noise on Japan's islands after the September 25, 2003, earthquake. This hypothesis is also supported by estimates of the measures of correlation and spectral coherence between variations in the average values of ∆α and α * calculated for 1-min data inside five spatial clusters of stations from consecutive time fragments two months long. Based on the well-known statement of the theory of catastrophes that synchronization is one of the flags of an approaching catastrophe, it was suggested that the Hokkaido event could be a foreshock of an even stronger earthquake nucleating in the region of Japan's islands. PACS numbers: 91.30.Ab
Synchronization of Microseismic Variations within a Minute Range of Periods
Izvestiya Physics of the Solid Earth
Records obtained at the Petropavlovsk, Yuzhno-Sakhalinsk, Magadan, Yakutsk, and Obninsk IRIS broadband stations before the Kronotski (Kamchatka) earthquake are investigated with the use of various programs of processing and analysis of time series. Intervals of a stable manifestation of one or several periods of microseisms (synchronization intervals) inferred from data of different stations do not necessarily coincide in time. No anomalous meteorological effects are recorded in these intervals. Geodynamic phenomena on global and regional scales influence the duration and intensity of the synchronization intervals. As distinct from other stations, the Petropavlovsk record revealed asymmetric variations of the relaxation type that arose five days before the Kronotski earthquake and three days before the onset of intense foreshock activation. The amplitude of variations at this station exceeds the level of other stations by an order of magnitude, which indicates that the source of this earthquake was located in the Pacific seismically active region. The number of predominant periods at the Petropavlovsk station decreases toward the time moment of the Kronotski earthquake, and the polymodal spectrum becomes unimodal, primarily due to the loss of shorter periods: a period of 37 min is most clearly expressed 1 h before the earthquake. The synchronization intervals of variations, as well as the foreshock activation, are indicators of the unstable state of a seismically active region.
The statistics of the time segments of low-frequency microseisms: Trends and synchronization
Izvestiya, Physics of the Solid Earth, 2010
The problem of identifying the effects of synchronization in the parameters of low frequency microseismic noise from the data of 77 stations belonging to the F net broadband seismograph network in Japan for the period from the beginning of 1997 through August, 2009 is considered. The vertical components measured initially with a sampling rate of one second and subsequently converted into the signals sampled at 1 minute intervals by means of averaging and decimation are used in the analysis. Six statistics are taken as the parameters: the support width of the multifractal singularity spectrum; the generalized Hurst exponent; the asymmetry coefficient of the spectrum of singularity; the logarithmic variance; the spectral exponent; and the linear predictability index. These parameters are calculated from the realizations contained within con secutive daily time intervals. When using the moving time window with a width of one year for evaluating the multiple correlation, the daily variations in the median values of the statistics of the noise measured at five spatial clusters of stations exhibit a stable increase in the synchronization not long before the Hokkaido earth quake (September 25, 2003; M = 8.3), subsequently passing to the new level of high synchronization. Based on the analysis of the trends in the index of linear predictability it turned out possible to estimate the begin ning of the enhancement in the synchronization with rather high accuracy as the middle of 2002. The effect revealed for the variations in the different parameters of microseisms is an independent argument for the ear lier conclusion about the synchronization in the field of the microseismic noise on the Japan Islands.
Geoplanet: Earth and Planetary Sciences, 2010
Nearly all models of earthquake preparation are known to indicate magnification of the collective component in the behavior of geophysical fields in the preparation zone as the moment the earthquake occurrence is approached. The geophysical monitoring is aimed at the detection of the so-called synchronization signal in variations of different geophysical parameters, as well as its duration and frequency range.
Izvestiya, Physics of the Solid Earth, 2008
The paper generalizes the experience accumulated in studies of microseismic noise in the period range from 1 to 300 min observed during time intervals preceding a few strong earthquakes. This frequency range is the least studied and occupies an intermediate position between low frequency seismology and investigations of slow geophysical processes. The range includes oscillations induced by atmospheric and oceanic processes and various modes of the Earth's free oscillations excited by very strong earthquakes. The main attention in the paper is given to the background behavior of microseisms, which contains continuous present arrivals from near weak and far strong and moderate earthquakes. The paper focuses on the examination of synchronization effects arising in joint multivariate analysis of information from several stations with estimation of multifractal spectra of singularity and multidimensional spectral measures of coherent behavior of singularity spectral parameters. The problem of using the synchronization effects of microseismic background in the search for new precursors of strong earthquakes is discussed. PACS numbers: 91.30.Bi
Multifractal Parameters of Low-Frequency Microseisms
Geoplanet: Earth and Planetary Sciences, 2010
Low-frequency microseismic oscillations serve as an important source of information about processes proceeding in the crust, in spite of the fact that the main energy of these oscillations is caused by processes proceeding in the atmosphere and ocean, such as variations in the atmospheric pressure and the action of oceanic waves on the coast and shelf. The relation of low-frequency microseisms having periods of 5-500 s to the intensity of oceanic waves is comprehensively investigated in [Friedrich et al.]. The reverse influence of low-frequency microseisms with still longer periods (from several tens to a few hundreds of minutes) on atmospheric pressure variations due to slow wave-like deformations of the lithosphere were investigated in . Actually, the Earth's crust is a medium propagating the energy from atmospheric and oceanic processes, and since the transmitting properties of the crust depend on its state, the statistical properties of microseisms reflect changes in lithospheric properties.
Izvestiya, Atmospheric and Oceanic Physics, 2011
This paper presents a software technique for analyzing the multidimensional time series of microseismic oscillations on the basis of over 14 years of continuous observations, from early 1997 to February 2011, at F net (Japan) broadband seismic stations. An analysis of the multifractal parameters of low frequency microseismic noise allowed us to hypothesize, in as early as 2008, that Japanese Islands were approaching a large seismic catastrophe, the signature of which was a statistically significant decrease in the support width of the multifractal singularity spectrum. Subsequently, as new data became available and after some new sta tistics of microseismic noise (such as a logarithm of noise variance and an index of linear predictability) were included in joint analysis, we obtained some new results, indicating the facts that the parameters of the microseismic background had been increasingly synchronized (the synchronization process was estimated to start in mid 2002) and that the seismic danger had permanently grown. A cluster analysis of background parameters led us to conclude that in mid 2010 the islands of Japan entered a critically dangerous develop mental phase of seismic process. The prediction of the catastrophe, first in terms of approximate magnitude (mid 2008) and then in terms of approximate time (mid 2010), was documented in advance in a series of papers and in proceedings at international conferences.
Asymmetrical pulses, the periodicity and synchronization of low frequency microseisms
Journal of Volcanology and Seismology - J VOLCANOL SEISMOL, 2008
Seismic records of eight IRIS broadband stations were analyzed at distances of 70 to 7160 km from the magnitude 8.3 Hokkaido earthquake of September 25, 2003. The stations situated in the subduction zone recorded asymmetrical microseismic pulses lasting 3–10 min a few days before the earthquake. No such pulses were observed in the records of the stations situated outside the subduction zone. Similar pulses were also recorded before the magnitude 7.8 Kronotskii, Kamchatka earthquake of 1997. The pulses are hypothesized to have been caused by creeping movements. Synchronous oscillations of microseismic noise with periods of 1–3 h were recorded as far as 3000 km from the Hokkaido earthquake a few days before it occurred. The noise coherence measure increased for stations closer to the epicenter. The question of the source of this coherence remains open. These effects belong to the class of those occurring in dissipative metastable systems; parts of the terrestrial lithosphere during th...
Cluster analysis of low-frequency microseismic noise
Izvestiya, Physics of the Solid Earth, 2011
A method is proposed for describing low frequency microseismic noise from the network of broadband seismic stations in a large seismically active region of the Japan Islands. The median values of daily estimates from each station for seven parameters (three characteristics of the multifractal singularity spectra of the waveforms, their spectral exponents and the smoothness indices, the logarithmic variance and the lin ear predictability index) are used for the description. These parameters are determined for consecutive daily time intervals from the beginning of January 1997 through the end of February 2010. Since these parameters are taken as the median values of the estimates from each station, they are, actually, the integral statistics of the microseismic field. The present paper is the continuation of two previous works , where the effects of synchronization in the low frequency microseismic field on a large time scale were ana lyzed on the data from the F net stations. In the present work, the number of different "behavior modes" of the microseismic field are sought as the number of clusters in the optimal partition of the cloud of 7 dimen sional vector parameters, estimated within a moving time window with a width of 2 years. A new character istic of the geophysical field is introduced, namely, the notion of the cluster exponent, which is the power exponent in the dependence of the value of the compactness function of a cloud of vector parameters on the number of clusters in the optimal partition of this cloud. Previously, a relatively rapid increase was revealed in the level of synchronization of the microseismic field, which started in the middle of 2002 and lasted for approximately one year. The level of synchronization remains high up to now. During the past 4 years (taking into account the width (2 years) of the time window within which the estimates were made), the cluster expo nent exhibits a long trend which is similar to the shorter trend before the Hokkaido event (M = 8.3) that occurred on September 25, 2003. These facts, together with the pattern of variations in the coefficient of cor relation between two multifractal parameters of the field, suggest a hypothesis of the enhancement of the seis mic hazard in the region of the Islands of Japan from the second half of 2010.
Geoplanet: Earth and Planetary Sciences, 2010
Triggering and synchronization (i.e. adjustment of rhythms of oscillating objects due to their weak interaction) are encountered in various fields, from mechanics to biological and social processes. Thus, it is only natural that triggering and synchronization phenomena are observed in many geophysical fields, as the Earth is embedded in the oscillating field of different origin, with extremely wide range of frequencies, from seconds to months and years. There are a lot of observations on the significant impact of small external forcing on the seismic regime, namely on the seismicity induced by: tides, reservoir exploitation, big explosions, magnetic storms, strong electrical pulses, wave trains of remote strong earthquakes, oceanic microseisms, etc, which means that these phenomena are connected with nonlinear interactions of objects, namely with initiation of instability in systems that are close to the critical state.