首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
We have analyzed the data on the times and number of weak earthquakes (M = 0–2.5) included in the up-to-date (final version) Catalog of Kamchatka Earthquakes for 1995–2008, and the intensity of highfrequency underground noise measured in the deep borehole near Petropavlovsk-Kamchatskiy (according to the literature data). We calculated the spectra of the seismic time series within the range of periods from 1 to 48 hours with a step of one minute. It was found that the spectrum of the earthquake data series contains a significant high Q extremum in a period of 24 hours that can be linked with a similar period in the high-frequency underground noise in Kamchatka and in the Russian Platform. There are some grounds to suggest that the weak earthquakes and the underground noise (seismoacoustic emission) have the same nature. In both cases, the shapes of the curve of the diurnal periodicity are found to depend on the duration of light during the day. The probable reasons for the solar impact on the seismic emission processes are discussed.  相似文献   

2.
Investigation and understanding of the present-day geodynamic situation are of key importance for the elucidation of the laws and evolution of the seismic process in a seismically active region. In this work, seismic moments of nearly 26000 earthquakes with K p ≥ 7 (M LH ≥ 2) that occurred in the southern Baikal region and northern Mongolia (SBNM) (48°–54°N, 96°–108°E) from 1968 through 1994 are determined from amplitudes and periods of maximum displacements in transverse body waves. The resulting set of seismic moments is used for spatial-temporal analysis of the stress-strain state of the SBNM lithosphere. The stress fields of the Baikal rift and the India-Asia collision zone are supposed to interact in the region studied. Since the seismic moment of a tectonic earthquake depends on the type of motion in the source, seismic moments and focal mechanisms of earthquakes belonging to four long-term aftershock and swarm clusters of shocks in the Baikal region were used to “calibrate” average seismic moments in accordance with the source faulting type. The study showed that the stress-strain state of the SBNM lithosphere is spatially inhomogeneous and nonstationary. A space-time discrepancy is observed in the formation of faulting types in sources of weak (K p = 7 and 8) and stronger (K p ≥ 9) earthquakes. This discrepancy is interpreted in terms of rock fracture at various hierarchical levels of ruptures on differently oriented general, regional, and local faults. A gradual increase and an abrupt, nearly pulsed, decrease in the vertical component of the stress field S v is a characteristic feature of time variations. The zones where the stress S v prevails are localized at “singular points” of the lithosphere. Shocks of various energy classes in these zones are dominated by the normal-fault slip mechanism. For earthquakes with K p = 9, the source faulting changes with depth from the strike-slip type to the normal-strike-slip and normal types, suggesting an increase in S v . On the whole, the results of this study are well consistent with the synergism of open unstable dissipative systems and are usable for interpreting the main observable variations in the stress-strain state of the lithosphere in terms of spatiotemporal variations in the vertical component of the stress field S v . This suggests the influence of rifting on the present-day geodynamic processes in the SBNM lithosphere.  相似文献   

3.
Immediately following the M S7.0 Lushan earthquake on April 20, 2013, using high-pass and low-pass filtering on the digital seismic stations in the Shanxi Province, located about 870–1,452 km from the earthquake epicenter, we detected some earthquakes at a time corresponding to the first arrival of surface waves in high-pass filtering waveform. The earthquakes were especially noticed at stations in Youyu (YUY), Shanzizao (SZZ), Shanghuangzhuang (SHZ), and Zhenchuan (ZCH), which are located in a volcanic region in the Shanxi Province,but they were not listed in the Shanxi seismic observation report. These earthquakes occurred 4–50 min after the passage of the maximum amplitude Rayleigh wave, and the periods of the surface waves were mainly between 15 and 20 s following. The Coulomb stresses caused by the Rayleigh waves that acted on the four stations was about 0.001 MPa, which is a little lower than the threshold value of dynamic triggering, therefore, we may conclude that the Datong volcanic region is more sensitive to the Coulomb stress change. To verify, if the similar phenomena are widespread, we used the same filtering to observe contrastively continuous waveform data before, and 5 h after, the M S7.0 Lushan earthquake and M S9.0 Tohoku earthquake in 2011. The results show that the similar phenomena occur before the earthquakes, but the seismicity rates after the earthquakes are remarkably increased. Since these weak earthquakes are quite small, it is hard to get clear phase arrival time from three or more stations to locate them. In addition, the travel time differences between P waves and S waves (S–P) are all less than 4 s, that means the events should occur in 34 km around the stations in the volcanic region. The stress of initial dynamic triggering of the M S9.0 Tohoku earthquake was about 0.09 MPa, which is much higher than the threshold value of dynamic triggering stress. The earthquakes after the M S9.0 Tohoku earthquake are related to dynamic triggering stress, but the events before the earthquake cannot be linked to seismic events, but may be related to the background seismicity or from other kinds of local sources, such as anthropogenic sources (i.e., explosions). Using two teleseismic filtering, the small background earthquakes in the Datong volcanic region occur frequently, thus we postulate that previous catalog does not apply bandpass filter to pick out the weak earthquakes, and some of the observed weak events were not triggered by changes in the dynamic stress field.  相似文献   

4.
Universality of the Seismic Moment-frequency Relation   总被引：1，自引：0，他引：1  
—We analyze the seismic moment-frequency relation in various depth ranges and for different seismic regions, using Flinn-Engdahl's regionalization of global seismicity. Three earthquake lists of centroid-moment tensor data have been used the Harvard catalog, the USGS catalog, and the Huang et al. (1997) catalog of deep earthquakes. The results confirm the universality of the β-values and the maximum moment for shallow earthquakes in continental regions, as well as at and near continental boundaries. Moreover, we show that although fluctuations in earthquake size distribution increase with depth, the β-values for earthquakes in the depth range of 0–500 km exhibit no statistically significant regional variations. The regional variations are significant only for deep events near the 660 km boundary. For declustered shallow earthquake catalogs and deeper events, we show that the worldwide β-values have the same value of 0.60 ± 0.02. This finding suggests that the β-value is a universal constant. We investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity (the number of earthquakes above a certain threshold level per year). The high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones. Combined with the universality of the β-value, this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones. If we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient, χ, is close to 100% for shallow seismicity, then we can estimate χ for deeper earthquakes for intermediate earthquakes χ≈ 5%, and χ≈ 1% for deep events. These results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard.  相似文献   

5.
We explore fractal properties of two observed seismicity distributions prior to the 2003 M w 7.4 Colima, Mexico and 1992 M w 7.3 Landers, USA earthquakes, together with several mathematical fractal distributions and two non-fractal ones, in order to estimate minimum reliable sample sizes, determine whether fractality for observed seismicity is essentially different from random uniform distributions, and explore the possibility of extracting premonitory information from fractal characteristics of seismicity before large earthquakes. Sample sizes above 800 events for whole catalogs appear to be sufficient to maintain ordered multifractality and to yield dimension estimates that vary smoothly and reliably. Fractal estimates appear to be best for whole catalogs that include aftershocks. The fractal characteristics of spatial distributions of seismicity are essentially different from those of the uniform random distribution, which is the null hypothesis of a non-fractal distribution with minimum information. The fractal dimensions and afractality measures of seismicity distributions change with time and show distinctive behaviors associated with foreshocks and main events, although these behaviors are different for each example. Results suggest the possibility of a priori identification of foreshocks to large earthquakes. A combination of fractal dimension and afractality measures over time may be helpful in large earthquake premonitory studies.  相似文献   

6.
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.  相似文献   

7.
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.  相似文献   

8.
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.  相似文献   

9.
The responses of the Kamchatka earthquakes with a minimum energy class of completeness K ≥ 8.5 to 214 strong worldwide earthquakes with magnitudes M ≥ 7.5 and to 40 earthquakes with M ≥ 8 are studied. The analysis covers the time interval of 1963–2012. The distances from the sources of the strongest earthquakes to the center of the seismically active Kamchatka zone range from 600 to 16000 km. It is established that the remote earthquakes enhanced seismic activity in Kamchatka, at least in the cases when the dynamic strain was above 10?6, which corresponds to the additional stresses of 10?2 MPa, accelerations above 0.1 cm/s2, and the periods of the surface waves of ～20 s. The response to the remote events gradually increased within a few days. The sensitivity of the response to the remote earthquakes varied in the course of time, which is identified on the intervals of a few dozens of years.  相似文献   

10.
A rational choice of the scalar seismic moment and ordering index is proposed that can be advantageously used for the monitoring of source zones of strong earthquakes in order to predict the development of a seismic situation. These parameters are the main characteristics of seismotectonic deformation. The ordering index characterizes a regular change in time of chaotization and ordering phases of the seismic process related to the occurrence of strong aftershocks. Using the December 5, 1997, Kronotskii (M w = 7.8) and December 26, 2004, Sumatra (M w = 9.0) earthquakes as an example, temporal variations of the studies parameters in the aftershock zones of these earthquakes are analyzed in detail.  相似文献   

11.
王伶俐  洪敏  张勇  高涵  徐良叶  牛甜 《中国地震》2020,36(1):91-104
采用GAMIT/GLOBK软件对云南境内及邻区近400个GNSS测点1999～2018年的观测数据进行解算,在各个测点时间序列和速度场的基础上,采用克里金插值方法分时段估计该区域在1999～2004年、2004～2007年、2009～2013年、2013～2015年、2015～2018年共计5个时间区域应变率场;根据区域地壳面应变率和最大剪应变率的空间变化以及相应时段之后3年内的MS≥5. 0地震事件分布特征,分析发现:绝大部分震例发生在面应变高梯度带的张压转换区和最大剪应变高值区,可见研究区各个观测时段GNSS应变率场对后期1～3年内的中强震发生区域有一定的指示意义;以2014年盈江6. 1级、鲁甸6. 5级和景谷6. 6级地震为样本,建立监视块体获取应变时间序列,分析发现:地震前三个月左右均出现震中附近短期应变趋势改变、快速增强、转折的现象,这些形变异常变化或许反映了发震区应力-应变积累在接近临界破裂状态时的非线性调整,为地震短临预测尤其是时间要素的判断提供参考。  相似文献   

12.
The depth changes in the b-value and density of the number of earthquakes in different magnitude bins (M ≥ 1.8, M ≥ 3.0, M ≥ 3.5) are analyzed using highly accurate seismological observations carried out in 1955–1991 at the Garm prognostic area in Tadjikistan. It is found that the observed b-values are controlled by the variations in the proportion between weak and strong earthquakes. Two horizons with different patterns of the b-value are identified in the Earth’s crust above and below a depth of 15–16 km. The b-value in the upper and lower horizons is close to 0.8 and 1.2, respectively. The lower horizon is marked by almost complete absence of relatively strong earthquakes with M ≥ 3.0. The observed changes in the b-value with increasing depth could probably be due to the increase in the strength of crustal material caused by the growth in temperature and confining pressure in the depth interval from 0 to 15 km. The transitional interval between the upper and lower crustal horizons (～13–18 km), which is characterized by a sharp drop in seismic activity, can probably be associated with the zone of the phase transition of crustal material from an elastic brittle state to a plastic state, as suggested by some authors. Typically, the top of this zone hosts the hypocenters of the strongest earthquakes in a given territory. The correlation is established between the crustal areas with low b-values and the locations of the strongest earthquakes in the region. It is suggested that the three-dimensional mapping of the b-value can be helpful for estimating the location, depth, and maximal magnitude of the probable strong earthquakes in seismically active regions and can be used to assess seismic risks.  相似文献   

13.
Mexico City high plasticity clays exhibit a small degree of nonlinearity for shear strains as large as 0.1%, which leads to both moderate shear stiffness degradation and small to medium damping increment, even for long duration subduction strong ground motions, such as the 8.1Mw 1985Michoacan earthquake. Nonetheless, current seismic design criteria of strategic infrastructure used worldwide have striven for having larger return periods for establishing the seismic environment, considering recent large magnitude (M>8.5Mw) events. This paper presents the study of the seismic response of typical high plasticity clays found in the so-called Texcoco Lake, in the surrounding of Mexico City valley, for larger to extreme earthquakes. The shear wave velocity profile was characterized using a down-hole test. The seismic environment was established from a set of uniform hazard response spectra developed for a nearby rock outcrop for return periods of 125, 250, 475 and 2475 years. A time-domain spectral matching was used to develop acceleration time histories compatible with each uniform hazard response spectrum. Both frequency and time domain site response analyses were carried out considering each seismic scenario. Ground nonlinearities were clearly observed in the soil response during extreme ground shaken, which increases rapidly with the return period. This fact must be taken into account to avoid costly and potentially unsafe seismic designs.  相似文献   

14.
Love waves from five earthquakes in southwest Germany, Italy, Yugoslavia, Greece and Algeria, as recorded at the broadband Gräfenberg array in eastern Bavaria, are modelled in detail using an extended reflectivity method. The focal mechanisms are taken from the literature or determined from long-period WWNSS data. The theoretical double-couple moment function used for modelling increases smoothly during the risetime T from zero to the seismic moment M0. T and M0 are determined by matching the observed and theoretical Love-wave seismograms in the long-period WWNSS frequency band. T is approximately equal to the rupture duration; values from 1.4 to 20 s are found. Seismic moments generally agree within a factor of about two with those found by other authors from larger data sets. The earthquakes in southwest Germany and Greece were simple events and can be modelled very well by one double couple. In the case of the other earthquakes, the theoretical Love-wave seismograms are too short. For these earthquakes there is some independent evidence for a multiple-event nature. This evidence is condensed into source models consisting of two or three double couples representing separate and complete sub-earthquakes, which then explain the observations quite well. In the case of the Algerian earthquake, the long Love-wave duration may also be due to complications in structure along the wavepath across the Mediterranean and the Alps. The present results show that accurate Love-wave modelling for a single station at regional distance from an epicentre is a reliable method for estimation of seismic moment and rupture duration. Use of a digitally recording station with large dynamic range allows events over a large magnitude interval to be studied. The Gräfenberg array is well suited for such an investigation of European and North African earthquakes.  相似文献   

15.
An earthquake ofM S=6.9 occurred at the Gonghe, Qinghai Province, China on April 26, 1990. Three larger aftershocks took place at the same region,M S=5.5 on May 7, 1990,M S=6.0 on Jan. 3, 1994 andM S=5.7 on Feb. 16, 1994. The long-period recordings of the main shock from China Digital Seismograph Network (CD-SN) are deconvolved for the source time functions by the correspondent recordings of the three aftershocks as empirical Green’s functions (EGFs). No matter which aftershock is taken as EGF, the relative source time functions (RSTFs) obtained are nearly identical. The RSTFs suggest theM S=6.9 event consists of at least two subevents with approximately equal size whose occurrence times are about 30 s apart, the first one has a duration of 12 s and a rise time of about 5 s, and the second one has a duration of 17 s and a rise time of about 8 s. Comparing the RSTFs obtained from P- and SH-phases respectively, we notice that those from SH-phases are a slightly more complex than those from P-phases, implying other finer subevents exist during the process of the main shock. It is interesting that the results from the EGF deconvolution of long-period wavform data are in good agreement with the results from the moment tensor inversion and from the EGF deconvolution of broadband waveform data. Additionally, the two larger aftershocks are deconvolved for their RSTFs. The deconvolution results show that the processes of theM S=6.0 event on Jan. 3, 1994 and theM S=5.7 event on Feb. 16, 1994 are quite simple, both RSTFs are single impulses. The RSTFs of theM S=6.9 main shock obtained from different stations are noticed to be azimuthally dependent, whose shapes are a slightly different with different stations. However, the RSTFs of the two smaller aftershocks are not azimuthally dependent. The integrations of RSTFs over the processes are quite close to each other, i. e., the scalar seismic moments estimated from different stations are in good agreement. Finally the scalar seismic moments of the three aftershocks are compared. The relative scalar seismic moment of the three aftershocks deduced from the relative scalar seismic moments of theM S=6.9 main shock are very close to those inverted directly from the EGF deconvolution. The relative scalar seismic moment of theM S=6.9 main shock calculated using the three aftershocks as EGF are 22 (theM S=6.0 aftershock being EGF), 26 (theM S=5.7 aftershock being EGF) and 66 (theM S=5.5 aftershock being EGF), respectively. Deducing from those results, the relative scalar sesimic moments of theM S=6.0 to theM S=5.7 events, theM S=6.0 to theM S=5.5 events and theM S=5.7 to theM S=5.5 events are 1.18, 3.00 and 2.54, respectively. The correspondent relative scalar seismic moments calculated directly from the waveform recordings are 1.15, 3.43, and 3.05.  相似文献   

16.
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.  相似文献   

17.
The variations in the intensity of the global seismic process during the 20th and beginning of the 21st centuries are analyzed. It is established that the evolution of the global seismic process is marked by a trend of a certain quasi-periodicity in the release of seismic energy. The analysis of the lithospheric seismicity during 113 years has shown that this time interval accommodated three periods of seismic activation separated by two periods of relative seismic quiescence. The global seismicity of the Earth is strongly dominated by the contributions of the earthquakes in the Pacific seismic belt. A considerable effect is also provided by the northeastern margin of the Indian Ocean. The horizontal displacements of the lithospheric plates are probably responsible for the accumulation of stresses in the potential sources of the earthquakes at the interplate contacts and in the orogenic areas inside the continents. The revealed clustering of the earthquakes with M ≥ 8.3 in the narrow time intervals is probably due to the fact that the strongest seismic event that occurs at the beginning of each activation is a trigger which simultaneously causes the relaxation of a few dozen mature potential sources within 10–15 years. This interval of seismic activation is followed by a relatively quiet period of 30–35 years, when the energy for the next activation is accumulated in a series of high-magnitude sources.  相似文献   

18.
The Hsingtai, China earthquakes of March 1966 were a series of destructive earthquakes associated with the Shu-lu graben. Five strong shocks of Ms ≥ 6 occurred within a period of less than a month, the largest of which was Ms 7.2. Body and surface waves over the period range from several to 100 s have been modeled for the four largest events using synthetic seismograms in the time domain and spectral analysis in the frequency domain. Data from ground deformation, local geology, regional seismic network, and teleseismic joint epicenter determination have also been used to constrain the source model and the rupture process.The fault mechanism of the Hsingtai sequence was mainly strike-slip with a small component of normal dip-slip. The strikes of the four largest shocks range from ～ N26° to 30°E, approximately along strike of the major faults of the Shu-lu graben and the aftershock distribution. The source mechanisms can be explained with a NNW-SSE extensional stress and a NEE-SWW compressional stress acting in the area. The major shocks all had focal depths ～ 10 km.The four largest shocks in the sequence were characterized by a relatively simple and smooth dislocation time history. The durations of the far-field source time functions ranged from 3.5 to 5 s, while the rise times were all ～ 1 s. The seismic moments of the four largest earthquakes ranged from 1.43 × 1025 to 1.51 × 1026 dyne cm?1. The fault sizes of the four events were very close. Assuming circular faults, the diameters of the four events were determined to be between 10 and 14 km. Stress drops varied from ～ 52 to 194 bars. A trend of increasing stress drop with earthquake size was observed.A survey of stress drop determinations for 15 major intraplate earthquakes shows that on the average the magnitude of stress drop of oceanic intraplate earthquakes and passive continental margin events is higher (～ 200 to several hundred bars) than that of continental intraplate earthquakes (～ 100 bars or less).  相似文献   

19.
In recent years, a large number of quarry blasts have been detonated in the eastern Black Sea region. When these blasts are recorded by seismic stations, they contaminate the regional earthquake catalog. It is necessary to discriminate quarry blast records from the earthquake catalogs in order to determine the real seismicity of the region. Earthquakes and quarry blasts can be separated through different methods. These methods should be applied concurrently in order to safely distinguish these events. In this study, we discriminated quarry blasts from earthquakes in the eastern Black Sea region of Turkey. We used 186 seismic events recorded by the Karadeniz Technical University and Bogaziçi University Kandilli Observatory Earthquake Research Institute stations which are Trabzon, Espiye, Pazar, Borçka, Ayd?ntepe, and Gümü?hane between years of 2002 and 2010. For the discrimination of quarry blasts from earthquakes, we used both, statistical methods (calculation of the maximum ratio of S to P waves (S/P), complexity (C)) and spectral methods (spectrogram calculation). These methods included measuring the maximum amplitude S/P, C, spectral ratio, and time-frequency analysis. We especially relied on two-dimensional time-frequency analysis methods to discriminate quarry blasts from earthquakes in Turkey. As a result of this study, 68 % of the examined seismic events were determined to be quarry blasts and 32 % to be earthquakes. The earthquakes occurring on land are related to small faults and the blasts are concentrated in large quarries. Nearly 40 % of the earthquakes occurred in the Black Sea, most of them are related to the Black Sea thrust belt, where the largest earthquake was observed in the time period studied. The areas with the largest earthquake potential in the eastern Black Sea region are in the sea.  相似文献   

20.
This is an attempt to analyze the current lithospheric stress pattern in the Baikal rift in terms of nonlinear dynamics as an open self-organizing system in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 MLH ≥ 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the system evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ≈ 7 events may happen in the region within a few years.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号