Diurnal periodicity of the representative earthquakes in Greece

The diurnal periodicity of seismic events of different energy from the Greece earthquake catalog was studied. Earthquake samplings of different energy with a known level of magnitude of completeness were compiled. Parameters of the diurnal periodicity of earthquakes in different time and magnitude intervals were analyzed. Significant diurnal periodicity of earthquakes with M ≤ 4.1 was revealed. The most important result of the paper is the discovery of the diurnal periodicity of the representative earthquakes with M = 3.2–4.1. The diurnal periodicity of representative earthquakes cannot be explained at the base of the prevailing hypothesis considering the diurnal periodicity of earthquakes as an apparent phenomenon resulting from diurnal changes in the real sensitivity of the seismic network due to diurnal variations of seismic noise.     

Changes in the diurnal periodicity of Southern California earthquakes in the neighborhood of the catalog magnitude of completeness

Dependence of the diurnal periodicity phase diagrams for Southern California earthquakes on their magnitude is studied with the Rayleigh-Schuster method. The highest statistical significance of diurnal periodicity is characteristic for the weakest non-representative earthquakes occurring in the night rather than in the daytime. The statistical significance of the earthquake diurnal periodicity decreases as the earthquake magnitude increases. Diurnal periodicity disappears in the neighborhood of the catalog magnitude of completeness. It appears again with a reasonably high level of statistical significance in the magnitude range exceeding the magnitude of completeness. However, its phase becomes opposite: strong earthquakes are more frequent in the daytime. Phase diagrams of different spatial earthquake sample groups are compared, and the night and daytime earthquake recurrence graphs are studied.     

Diurnal periodicity of earthquakes and its seasonal variations

Analysis of earthquake catalogues on 14 world regions has revealed a distinct diurnal periodicity of seismic events in all of them. The amplitude of the diurnal variations usually decreases with an increase in earthquake energy, although in some regions, the time series of strong earthquakes also demonstrate diurnal periodicity. Earthquakes are more frequent at night. The acrophase of the course of diurnal seismicity correlates with geographic longitude. The Rayleigh — Schuster hodographs of diurnal periodicity demonstrate sharp changes (kinks) in the vicinity of the equinox and solstice moments. The annual hodograph of the diurnal periodicity of earthquakes is distinctly divided by the equinox moments into segments with different slopes. The defined segments differ in the amplitude and acrophase of the course of diurnal seismicity. The data imply influence of the mutual positions of the Sun and Earth on seismicity in different world regions. Possible mechanisms responsible for such influence are discussed.     

On the causes of unordinary periodicity of earthquakes

The diurnal periodicity of seismic events from three earthquake catalogs of Fennoscandia and Turkey is studied. The shape of diurnal distribution of seismic events in all the catalogs under investigation is similar to the unordinary diurnal periodicity of earthquakes described in previous papers. The principal feature of the diurnal periodicity of seismic events revealed in this paper is a wide maximum of the events in the day time. The very reliable conclusion is made that it is caused by presence of a great amount of quarry blasts in the catalogs.     

Diurnal periodicity of earthquakes in Greece

The catalog of earthquakes that happened in Greece over the period of 1964 to 2008 was used for the analysis of their diurnal periodicity in this region. The quality of the catalog was examined with the defining of the representativeness levels of earthquakes in different selections. The earthquakes, including relatively strong events with the magnitude M ≥ 4.0, demonstrate diurnal periodicity with seasonal differences in their course reflected in their higher summer seismicity as compared with the winter one.     

Estimating the number of blasts in the Dushanbe-Vakhsh earthquake catalog

The daily periodicity in four regions of the Dushanbe–Vakhsh area is analyzed. The study considers representative, nonrepresentative, and intermediate-energy earthquakes. Analysis of the specific features of the shape of the diurnal variation on workdays and weekends make it possible (1) to reliably conclude that the anomalous daily variation on workdays in medium-energy earthquake samplings is of technogenic origin and (2) suggest similarities in samplings of the weakest and strongest earthquakes. Apparently, the catalog includes a large number of industrial blasts. The number of blasts in earthquake samplings of various epochs and energies is estimated.     

Diurnial periodicity of strong earthquakes of Garm research area

The diurnial periodicity of Garm Polygon earthquakes of various energy classes K [(magnitudes M): weak, K < 6.0 (M < 1.1); moderate, 6.0 < K < 8.0 (1.1 < M < 2.2); strong, K > 8.0 (M > 2.2)] has been studied. The time series of weak earthquakes is characterized by maximum activity at night and a clear diurnal periodicity that practically disappears for moderate earthquakes. Such periodicity can be traced again in the time series of the strong earthquakes practically antiphased to weak earthquakes; i.e., the maximum strong earthquakes occurred during the day time.     

Search for Technogenic Effects in the Time Series of Earthquakes in Greece

A search for technogenic effects in the time series of earthquakes in Greece is carried out. The ine- quality of intra-week distributions of earthquakes including the events of M ≥ 3.7 is shown. Sharp changes in the pattern of Rayleigh-Schuster’s hodograph for the diurnal periodicity of earthquakes were revealed. They are located in the time vicinity of the moments of the equinox. The result supports the idea of the natural gen- esis of the diurnal periodicity of earthquakes and the important role of the Sun.     

Comments on the European Macroseismic Scale (EMS-98) in Terms of Its Applicability in Russia

A search for technogenic effects in the time series of earthquakes in Greece is carried out. The ine- quality of intra-week distributions of earthquakes including the events of M ≥ 3.7 is shown. Sharp changes in the pattern of Rayleigh-Schuster’s hodograph for the diurnal periodicity of earthquakes were revealed. They are located in the time vicinity of the moments of the equinox. The result supports the idea of the natural gen- esis of the diurnal periodicity of earthquakes and the important role of the Sun.     

Comparison of the diurnal periodicity features of seismic noise,earthquakes, and electric power consumption

The main features of periodic changes in the parameters of seismic noise, seismicity and electric power consumption in industrial networks are compared to verify the hypothesis on the technogenic influence of electric network load on seismic noise and seismicity and to search for possible origins of the diurnal periodicity in seismic emission processes discovered in various regions of the world. Sufficiently good similarity of the compared processes is revealed that does not contradict the hypothesis. However, there are also some important discrepancies. An inverse phase pattern of interdiurnal distributions of weak and strong Japanese earthquakes has been found, and various possible mechanisms of this phenomenon, which had been observed earlier in certain other regions, are discussed.     

东北地区地震活动的Rydelek-Sacks周期性检验和震级-周期谱研究

为检验中国东北地区地震活动可能存在的周期性特征和深、浅源地震在周期性活动上的相关性,利用Rydelek-Sacks检验方法和不同的地震目录,考虑了地震震级的选取对周期性特征识别可能存在的影响,并在震级-周期谱中进行了比较研究.对该地区1970-2009年ML≥4.5浅源地震、1920-2009年Ms≥5.0浅源地震和1...     

Search for tidal seismicity in Greece using different techniques: Part 3. Correlation with solar and lunar tidal waves

The last of a cycle of three papers aimed at searching for the influence of the gravitational tide on regional Greece seismicity using different techniques is presented. Twenty-five nonintersecting samplings of earthquakes in Greece compiled from events with different energy and time intervals were studied in the two previous papers (Desherevskii and Sidorin, 2012d, 2014). Stable diurnal and semidiurnal periodicities (24:00 and 12:00 h) were revealed in the seismicity spectra. Periodicities with a small amplitude with periods close to M₂ and O₁ tidal waves were also found in some samples. The correlation coefficients of all time series of earthquakes were calculated with the following theoretical tide parameters: volume deformation, strain rate, of strain rate modulus, and smoothed diurnal tidal amplitude. As the main result, stable significant correlation of seismicity was revealed with some tidal parameters. However, this could be the result of coincidence in periods of sub-harmonics of the diurnal seismicity rhythm with solar tidal waves. This means that the discovered correlation could simply be caused by the coincidence of two regular components in variations of the compared processes, but not with the gravitational tide. Correlations of seismic activity with solar and lunar tides are studied separately in this paper. This makes possible to separate the influence of gravitational and nongravitational factors. Strong correlation of seismicity was observed only with the solar tide. No stable correlation of seismicity with the lunar tide was revealed. The results can be considered evidence for the nongravitational origin of seismic activity variations that correlate with the tidal parameters. This means that tidal seismicity variations, if they are real, should have a much smaller amplitude in comparison with diurnal solar variations of nongravitational origin. Similar effects could cause wrong conclusions on the tidal influence on seismicity in some studies.     

Evaluation of a seismic damage parameter

Several parameters have been proposed in the literature for the evaluation of seismic damage. However, in most cases the correlation between results obtained using these parameters and observed damage in structures has not been satisfactory. A parameter for measuring seismic damage previously proposed by the first author is used in this study to analyse a set of 15 accelerograms recorded in 11 earthquakes experienced in different countries. Results using this parameter are compared to global building damage observed during these earthquakes. The use of the parameter proposed here yields results which are consistent with building damage observed in the earthquakes studied. Copyright © 1999 John Wiley & Sons, Ltd.     

Search for tidal seismicity in Greece using different techniques: Part 2. Correlation analysis

In the first part of this paper (Deshcherevskii and Sidorin, 2012b), the spectra and periodograms of time series of earthquakes in Greece were studied for various magnitude ranges and five calendar epochs. As the main result, the stable diurnal (24-h) and semidiurnal (12-h) periodicities of earthquakes were revealed. Periodicities of small amplitude related to tidal waves M₂ and O₁ were also revealed in some samplings. This part of the paper deals with the problems of searching for tidal effects in seismicity with traditional techniques. An alternative approach of the task is applied. The time series of earthquakes with various magnitude and representativity (magnitude of completeness) were formed. Correlation coefficients of all the time series of earthquakes were calculated with the following theoretical tide parameters: volume deformation, strain rate, module of strain rate, and smoothed diurnal tidal amplitude. Stable significant correlation of seismicity was revealed with some tidal parameters. However, it can be a result of coincidence in periods of subharmonics of diurnal seismicity rhythm with the solar tidal waves. It means that the correlation discovered could be simply caused with coincidence of two regular components in variations of the compared processes but not with gravitational tide.     

Apparent stress scaling for tectonic and induced seismicity: Model and observations

A macroscopic model of seismic sources provides a scaling relationship for the apparent stress, treated as a function of three independent parameters: seismic moment, rupture area size, and average slip acceleration. These parameters represent three different factors: kinematic, geometric and material. This relationship allows us to distinguish and explain the following statistical characteristics of the log apparent stress versus log seismic moment plot. The regional trends, represented by a series of 1/2 slope lines, are related to the averaged shape of slip velocity pulses, so they reflect kinematic characteristics of the rupture process. The global trend, represented by the 1/6 slope line, is expected to characterize sets of events of wide range of rupture area sizes and assumes dependence of rupture area size on total slip, so it is related to the rupture initiation, propagation and arrest conditions; therefore, it reflects earthquake rupture dynamics. Additional shiftings among the trend lines obtained for the smallest induced tremors, larger tectonic earthquakes, and slow tsunami earthquakes, reflect differences between the intact rock failure and the frictional slip failure, that is, between fracture energies of these different earthquake classes.     

Andaman-Sumatra island arc: 1. Spatiotemporal manifestations and focal mechanisms of the earthquakes

The spatiotemporal manifestations of seismicity in the Andaman-Sumatra island arc are studied using the instrumental data for 1900–2010. The data on the largest tsunamigenic earthquakes of the 18th–19th centuries were also taken into account. The epicenters of the earthquakes are established to cluster in some areas; their possible relation to the structural features of the island arc is considered. A distinctive feature of seismicity in the region of the Andaman Sea is the presence of compact swarms of numerous earthquakes occurring during short intervals of time. The distribution of the earthquakes by the depth of their hypocenters in different segments of the island arc is investigated. The focal mechanisms of the earthquakes are analyzed using the centroid-moment-tensor (CMT) determinations over the period of 1980–2004, and the characteristic features of their parameters in different segments of the Andaman-Sumatra island arc are formulated. The focal parameters of the earthquakes determined by CMT and the moment-tensor-solution (MTS) are compared; the possible uncertainty in the estimates of the focal mechanisms is assessed. The pattern of the spatiotemporal manifestations of the Andaman-Sumatra earthquakes and their focal mechanisms are compared to the data on the Kuril-Kamchatka and the Aleutian island arcs previously studied by the authors. The results of analyzing the long-term seismicity and focal mechanisms in the Andaman-Sumatra island arc provide a necessary basis for the further thorough investigation of the geological conditions and source parameters of the major Sumatra earthquakes of 2000–2010.     

The pattern of diurnal periodicity of weak earthquakes in Iran

The catalogue of earthquakes recorded in Iran during 2006–2010 by a dense network of digital telemetric seismic stations is analyzed. The spectrum of the time series of these earthquakes contains a sharp maximum at 24 h. The corresponding curve of diurnal periodicity constructed by the superposed epoch method has a clear double-peak maximum near noon(11 a.m.-5 p.m. local time), which exceeds the level of seismic activity observed during the rest time of the day by a factor of 3-3.5. In the same time interval, the average hourly magnitudes of seismic events sharply drop from M = 2.15 to M = 1.95. The ratio of the normalized number of earthquakes in the daytime to those at other times of the day, which was determined within a moving window half a square degree in size, has seven distinct compact spatially isolated maxima whose magnitudes attain several dozens to a hundred units. These maxima are probably caused by industrial activity, such as road building and quarry explosions. We also note the presence of the weekend effect when the daytime maximum in the weekly curve of diurnal variations in seismic activity almost completely disappears on Friday, which is the weekend in Muslim countries. At the same time, elimination of the supposed noise component from the catalogue by the approved technique changes nothing for the daytime maximum in the daily pattern of earthquakes in Iran. In order to account for this inconsistency, we suggest invoking additional information on the technogenic seismicity and considering weak earthquakes induced by quarry explosions and vibrations of industrial machines, in particular, power units of numerous hydroelectric power stations distributed over the territory of Iran.     

Diurnal periodicity of earthquakes in central Asia: Part 5. Catalogue of the Kyrgyz digital broadband seismic network KNET

Detailed analysis of the information contained in the earthquake catalogue of the Kyrgyz digital broadband seismic network over the period from 1994 to 2005 is performed. The graphs of earthquake recurrence were plotted and analyzed. The energy threshold of representativeness of the catalogue was determined. Stroboscopic and Fourier spectra of time series of earthquakes in the range of periods T ≤ 48 h are presented. A similarity between the obtained graph of diurnal course of seismicity with similar graphs for other regions was found. Peculiarities of diurnal course of earthquakes of different energy were studied. Earthquake sampling of the southwestern part of the territory presented in the catalogue was studied separately. Erroneous information in the catalogue caused by explosions is identified. A conclusion is made about a need for special measures to identify the explosions contained in the catalogue. Special algorithms for processing digital seismograms should be used in addition to collecting information about the time of explosions.     

Diurnal periodicity of weak earthquakes in Central Asia

Data on the time moments and numbers of weak earthquakes (M ≥ 0) are analyzed in five regions of Central Asia where long-term extensive instrumental observations of seismicity were conducted. Spectra of time moments of seismic events were calculated in the range of periods from 1 to 48 h with a step of half an hour. The time variations in the numbers of these earthquakes were also calculated in windows of 4 to 48 h wide with a summation step of 1 h. The presence of significant high-quality spectral extrema at periods of 24 and 12 h is established for all catalogs used, and less significant extrema at a period of 8 h are established for some catalogs. These periodicities are observed in the analysis of weak earthquakes with M < 2.2 (K < 8) and are virtually absent for stronger seismic events. It is shown that lunisolar tides have no appreciable gravitational effect on the observed variations in seismic emission. Daily variations in the actual sensitivity of the observation network due to the daytime increase in the noise level as a factor responsible for the observed diurnal periodicity raise doubts.     

大地震的18.6年周期

将全球分为15个研究区,用1900~2009年MW≥7.0地震目录,统计分析了各区大地震与月球交点运动周期的关系,得出15个研究区中有10个区,大地震存在统计意义上的18.6 a周期:活跃段为12.4 a,平静段为6.2 a;环太平洋地震带北、南、西、东4大区的大地震,不仅有这样的周期,而且其地震活跃段的时间存在一定规律.用第6个18.6 a(1991~2009年)期间的大地震,检验据前5个18.6 a(1900~1990年)地震目录所得18.6 a 周期的稳定性和实用性,发现有这种周期的地区多数的周期性是稳定的.大地震18.6 a周期的可能成因有: (1)18.6 a潮波通过调制日潮和半日潮调制大地震; (2)上地幔内流体的潮汐(地内潮)作用; (3)18.6 a潮波通过影响地球自转变化调制大地震.