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1.
The presence of a phenomenological relationship between high velocity regions in the Benioff zone and sources of relatively strong earthquakes (M ≥ 6) was established for the first time from the comparison of such earthquakes with the velocity structure of central Kamchatka in the early 1970s. It was found that, in the region with P wave velocities of 8.1–8.5 km/s, the number of M ≥ 6 earthquakes over 1926–1965 was 2.5 times greater than their number in the region with velocities of 7.5–8.0 km/s. Later (in 1979), within the southern Kurile area, Sakhalin seismologists established that regions with V P = 7.3–7.7 km/s are associated with source zones of M = 7.0–7.6 earthquakes and regions with V P = 8.1–8.4 km/s are associated with M = 7.9–8.4 earthquakes. In light of these facts, we compared the positions of M = 7.0–7.4 earthquake sources in the Benioff zone of southern Kamchatka over the period 1907–1993 with the distribution of regions of high P velocities (8.0–8.5 to 8.5–9.0 km/s) derived from the interpretation of arrival time residuals at the Shipunskii station from numerous weak earthquakes in this zone (more than 2200 events of M = 2.3–4.9) over the period 1983–1995. This comparison is possible only in the case of long-term stability of the velocity field within the Benioff zone. This stability is confirmed by the relationship between velocity parameters and tectonics in the southern part of the Kurile arc, where island blocks are confined to high velocity regions in the Benioff zone and the straits between islands are confined to low velocity regions. The sources of southern Kamchatka earthquakes with M = 7.0–7.4, which are not the strongest events, are located predominantly within high velocity regions and at their boundaries with low velocity regions; i.e., the tendency previously established for the strongest earthquakes of the southern Kuriles and central Kamchatka is confirmed. However, to demonstrate more definitely their association with regions of high P wave velocities, a larger statistics of such earthquakes is required. On the basis of a direct correlation between P wave velocities and densities, the distributions of density, bulk modulus K, and shear modulus μ in the upper mantle of the Benioff zone of southern Kamchatka are obtained for the first time. Estimated densities vary from 3.6–3.9 g/cm3 in regions of high V P values to 3.0–3.2 g/cm3 for regions of low V P values. The bulk modulus K in the same velocity regions varies from (1.4–1.8) × 1012 to (0.8–1.1) × 1012 dyn/cm2, respectively, and the shear modulus μ varies from (0.8–1.0) × 1012 to (0.5–0.7) × 1012 dyn/cm2, respectively. Examination of the spatial correlation of the source areas of southern Kamchatka M = 7.0–7.4 earthquakes with the distribution of elastic moduli in the Benioff zone failed to reveal any relationship between their magnitudes and the moduli because of the insufficient statistics of the earthquakes used.  相似文献   

2.
The temperature variations of the near-surface atmosphere in Kamchatka at Paratunka observatory and fluxes of outgoing infrared radiation prior to strong Kuril earthquakes (November 15, 2006, M = 8.3; January 13, 2007, M = 8.1) have been analyzed. It is shown that the radiation fluxes at ground level, as measured on satellites above the epicenter of earthquakes and above a remote observatory, coincide with each other, both in magnitude and in the feature of their time variations. The temperature measured directly at the observatory and the temperature at surface level estimated from satellite observations differ in magnitude, but they coincide in the feature of their time variations. The detected temperature increase (despite the negative regular trend at this time of year) is caused by the appearance of an additional heat source entering in the nearsurface atmosphere. This result, together with the studies of variations of various geophysical data before strong earthquakes performed earlier in Kamchatka, led to the conclusion that the additional heat source is in the Earth’s crust.  相似文献   

3.
We report extensive anomalies identified in seismicity parameters at different energy levels which were observed during the precursory process of the Karymskii seismovolcanic crisis of January 1–2, 1996. The seismicity of different energies includes earthquakes contained in the Kamchatka regional catalog and seismic noise (amplitudes of 10?9–10?12 m, frequencies of a few tens of hertz), which is a manifestation of the seismic process in the lowest energy range. The parameters of background seismicity are considered in retrospect using techniques for analyzing the dynamics of the seismic process: RTL and the Z function. Microseismicity is examined using these authors’ own method based on monitoring the response of high frequency seismic noise to tidal excitation  相似文献   

4.
A 56-year cyclicity in the occurrence of large Kamchatka earthquakes has been previously detected. This is another manifestation of the tendency for the timing of large Kamchatka earthquakes to be synchronized to the cycles related to the period T o of rotation of the lunar nodes found by V.A. Shirokov in 1974. He identified cycles of 18.6 years = T o and 6.2 years = T o/3, while the period of the 56-year cycle is 3T o. The genuineness of that phenomenon had to be revised in connection with the occurrence of a large (M w = 7.8) earthquake in Kamchatka at the end of 1997, in violation of the 56-year cyclicity. It turned out that, even though the 56-year cycle has become less distinct after the 1997 event, the cyclicity itself has remained statistically significant. A byproduct is an updated forecast of earthquake hazard for Kamchatka. The update is necessary in view of the approaching hazardous period of 2008–2011. It is found that, assuming the validity of these empirical tendencies, the expected rate of large earthquakes off Kamchatka for the period of August 2008 to October 2011 will be four times as high as the long-term mean. We derive the first-ever estimate of future hazard in terms of felt intensity for specified soil conditions (the so-called average soil) at a specified site (the town of Petropavlovsk-Kamchatskii). For these soil conditions, the estimated probability of at least one shock of intensity VII or greater during the period specified above is equal to 0.39 ± 0.15. The expected rate of single events or sets of events with M w ≥ 7.6 in Kamchatka during this period is 0.76 ± 0.25.  相似文献   

5.
—The 1952 Kamchatka earthquake is among the largest earthquakes of this century, with an estimated magnitude of M w = 9.0. We inverted tide gauge records from Japan, North America, the Aleutians, and Hawaii for the asperity distribution. The results show two areas of high slip. The average slip is over 3 m, giving a seismic moment estimate of 155×1020Nm, or M w = 8.8. The 20th century seismicity of the 1952 rupture zone shows a strong correlation to the asperity distribution, which suggests that the large earthquakes (M > 7) are controlled by the locations of the asperities and that future large earthquakes will also recur in the asperity regions.  相似文献   

6.
The paper continues the series of our works on recognizing the areas prone to the strongest, strong, and significant earthquakes with the use of the Formalized Clustering And Zoning (FCAZ) intellectual clustering system. We recognized the zones prone to the probable emergence of epicenters of the strongest (M ≥ 74/3) earthquakes on the Pacific Coast of Kamchatka. The FCAZ-zones are compared to the zones that were recognized in 1984 by the classical recognition method for Earthquake-Prone Areas (EPA) by transferring the criteria of high seismicity from the Andes mountain belt to the territory of Kamchatka. The FCAZ recognition was carried out with two-dimensional and three-dimensional objects of recognition.  相似文献   

7.
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   

8.
A pronounced increase in seismicity started in and around Longtan reservoir, southwestern China after October 1, 2006 when it began the impoundment, and by the end of May 14, 2010, about 3,233 earthquakes with ?0.6?≤?M L?≤?4.2 had been located. This seismicity which occurred in five clusters mainly concentrated in the areas where few earthquakes had occurred before the first filling. There were four water filling periods in the Longtan reservoir, and the observed reservoir-induced seismicity (RIS) shows a strong correlation with the filling cycles. After the first filling, there appears to be an instant undrained response due to an elastic response to the reservoir load in the third and fourth cluster. Then, this seismicity is followed by a delayed, drained response due to pore pressure diffusion, with the seismicity migrating outwards in one or more directions in the second and third filling period. The seismic diffusivity (α s) we estimated is about 4.54?×?105?cm2/s. The activity levels in the five clusters are different due to differences in the structures and permeabilities of the faults. The delayed seismic response to the filling in the third cluster was due to the combined effects of the lack of local fault intersecting the reservoir and lower permeability of the rock. The b value we obtained for reservoir-induced events was significantly different and higher than that of pre-impoundment natural tectonic earthquakes in the Longtan reservoir. The results of relocated earthquakes based on double difference earthquake location algorithm showed that their focal depths were mainly shallower than about 10 km and the distribution of relocated RIS in four clusters had no relation with these intersecting faults in the Longtan reservoir except the fifth cluster. All these characteristics of RIS in the Longtan reservoir indicate that they may relate to the coupled poroelastic response that includes both pore pressure diffusion and an undrained response, but the pore pressure diffusion and the water permeation appear to play a more important role on inducing the earthquakes in Longtan reservoir.  相似文献   

9.
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   

10.
The analysis of the existing information concerning the present-day deformation activity of the fault zones in seismically active and aseismic regions suggests that the notions of an active fault and a dangerous fault should be distinguished. It is shown that a fault which is active for an expert in geotectonics will not be considered dangerous by an expert in geotechnical monitoring of buildings. The definition is given according to which a dangerous fault is understood as a zone of linear destruction which accommodates the contemporary short-period (a few months and years) pulsed and/or alternating motions with strain rates above 5 × 10–5 per annum and earthquakes with M ≥ 5. A technique is developed for identifying the dangerous faults based on monitoring the recent ground surface displacements in accordance with a special protocol which ensures an increased degree of detail in time and space. Based on the idea of the probable accumulation of dangerous strains during the operating cycle of the objects, the criteria for assessing their geodynamical risks are formulated.  相似文献   

11.
Records of the IRIS broadband stations in Petropavlovsk-Kamchatski, Yuzhno-Sakhalinsk, Magadan, Yakutsk, Arti, and Obninsk obtained before the Kronotskii (Kamchatka Peninsula) M = 7.7 earthquake of December 5, 1997, and the Neftegorsk (Sakhalin Island) M = 7.0 earthquake of May 27, 1995, are investigated with the use of the Spectra Analyzer interactive program, designed for the analysis of properties of scalar time series. It is found that, 5 to 10 days before the shocks, stations nearest to the sources of these earthquakes recorded pulsed vibrations a few minutes long that were separated by intervals of a few tens of minutes. The shape asymmetry of the pulses characterized by different amplitudes of positive and negative polarity phases increased toward the earthquake onset time, as did the frequency and regularity of the pulse sequence. It is assumed that the nature of this phenomenon is related to self-organization properties of the seismic process in a metastable lithosphere and to the synchronization of vibrations in the inner and outer shells of the Earth, including chaotic and quasi-periodic components.  相似文献   

12.
Based on the analysis of the world’s earthquakes with magnitudes M ≥ 6.5 for 1960–2013, it is shown that they cause global-scale coherent seismic oscillations which most distinctly manifest themselves in the period interval of 4–6 min during 1–3 days after the event. After these earthquakes, a repeated shock has an increased probability to occur in different seismically active regions located as far away as a few thousand km from the previous event, i.e., a remote interaction of seismic events takes place. The number of the repeated shocks N(t) decreases with time, which characterizes the memory of the lithosphere about the impact that has occurred. The time decay N(t) can be approximated by the linear, exponential, and powerlaw dependences. No distinct correlation between the spatial locations of the initial and repeated earthquakes is revealed. The probable triggering mechanisms of the remote interaction between the earthquakes are discussed. Surface seismic waves traveling several times around the Earth’s, coherent oscillations, and global source are the most preferable candidates. This may lead to the accumulation and coalescence of ruptures in the highly stressed or weakened domains of a seismically active region, which increases the probability of a repeated earthquake.  相似文献   

13.
The ionospheric response to the transit of acoustic waves from a number of the strongest submarine earthquakes with magnitudes M w ≥ 7.7, which occurred during the past few years, is analyzed. The amplitude of the response in the detrended TEC is studied as a function of the magnitude and vertical component of the surface deformation. It is shown that the geomagnetic field can significantly modulate the shape of the ionospheric response, depending on whether the perturbation propagates equatorward or polarward.  相似文献   

14.
The time variations in the Gutenberg–Richter b-value are minutely studied based on the data of highly accurate seismological observations at the Garm prognostic site, Tajikistan, where a stationary network of seismic stations of the Complex Seismological Expedition (CSE) of Schmidt Institute of Physics of the Earth (IPE) of the USSR (Russian) Academy of Sciences was in operation from 1955 to 1992. A total of 93035 local earthquakes ranging from 0.0 to 6.3 in the Ml magnitudes are considered. The spatiotemporal fluctuations in the minimal magnitude of completeness of the earthquakes, Mc, are analyzed. The study considers a 25-year interval of the observations at the center of the observation system within which Mc = 0.9. It is shown that in most cases, the b-value and log10E2/3 experience characteristic time variations before the earthquakes with magnitudes higher than the minimal magnitude of the predicted earthquake (MPE). The 6-year anomaly in the parameters’ b-value, log10E2/3, and log10N associated with the single strongest earthquake with M = 6.3 that occurred in the observation region on October 26, 1984 is revealed. The inversely proportional relationship is established between the time variations in the b-value and the time variations in the velocities of seismic waves Vp and Vp/Vs. It is shown that the exponent p in the power function which links the time variations of the b-value and log10E2/3 is higher in the zones of crustal compression than in the zones of extension. It is simultaneously confirmed that the average b-value in the zones of compression is lower than in the zones of extension. It is established that in the case of earthquakes with M ≥ 2.6, the time series of seismic activity log10Ni and the time series of the b-value are highly cross correlated with a coefficient of r ≈ 0.75, whereas in the case of earthquakes with M ≥ 0.9, the coefficient of cross correlation between these time series is close to zero (r ≈ 0.06). The law of variations in the slope of the lines approximating the relationship between the log10Ni time series in the different magnitude ranges (M ≥ Mci) and b-value time series is obtained. It is hypothesized that the seismic activity of the earthquakes with high magnitudes can be estimated provided that the parameters of the time series of the b-value and time series of the number of earthquakes logN(ΔMi) in the range of low magnitudes are known. It is concluded that using the parameter log10N for prognostic estimates of the strong earthquakes only makes sense for earthquakes having moderate and large magnitudes. It is inferred that the time variations in the b-value are predominantly contributed by the time variations of the earthquakes with relatively large magnitudes.  相似文献   

15.
—This paper studies the source properties of earthquakes originating within the shallow subduction zone near Kamchatka Peninsula. We use the regional catalog of 1962–1993 Kamchatkan earthquakes completed by the Institute of Volcanology, Russia. Our previous investigations (Zobin, 1990, 1996a) and this study allow us to show a gradual change in source properties of earthquakes from trench to coast.¶It was demonstrated that the swarm sequences change to the mainshock–aftershock sequences from trench to coast. The source area of aftershock sequences is generally smaller than the swarm areas for the same magnitude M s of the mainshock or clue event of the swarm. Study of the M s –K s relation, where K s is the energy class for Kamchatka earthquakes, reveals that the events radiate relatively higher frequencies from trench to coast.  相似文献   

16.
To estimate the parameters of ground motion in future strong earthquakes, characteristics of radiation and propagation of seismic waves in the Kamchatka region were studied. Regional parameters of radiation and propagation of seismic waves were estimated by comparing simulations of earthquake records with data recorded by stations of the Kamchatka Strong Motion Network. Acceleration time histories of strong earthquakes (M w = 6.8–7.5, depths 45–55 km) that occurred near the eastern coast of Kamchatka in 1992–1993 were simulated at rock and soil stations located at epicentral distances of 67–195 km. In these calculations, the source spectra and the estimates of frequency-dependent attenuation and geometrical spreading obtained earlier for Kamchatka were used. The local seismic-wave amplification was estimated based on shallow geophysical site investigations and deep crustal seismic explorations, and parameters defining the shapes of the waveforms, the duration, etc. were selected, showing the best-fit to the observations. The estimated parameters of radiation and propagation of seismic waves describe all the studied earthquakes well. Based on the waveforms of the acceleration time histories, models of slip distribution over the fault planes were constructed for the studied earthquakes. Station PET can be considered as a reference rock station having the minimum site effects. The intensity of ground motion at the other studied stations was higher than at PET due to the soil response or other effects, primarily topographic ones. At soil stations INS, AER, and DCH the parameters of soil profiles (homogeneous pyroclastic deposits) were estimated, and nonlinear models of their behavior in the strong motion were constructed. The obtained parameters of radiation and propagation of seismic waves and models of soil behavior can be used for forecasting ground motion in future strong earthquakes in Kamchatka.  相似文献   

17.
Results are reported from the ongoing 2007–2008 work using the method of long-term earthquake prediction for the Kuril-Kamchatka arc based on the patterns of seismic gaps and the seismic cycle. This method was successful in predicting the M S = 8.2 Simushir I. (Middle Kuril Is.) earthquake occurring in the Simushir I. area on November 15, 2006. An M S = 8.1 earthquake occurred in the same area on January 13, 2007. We consider the evolution of the seismic process and determine the common rupture region of the two earthquakes. The sequence of M ≥ 6.0 aftershocks and forecasts for these are given. We provide a long-term forecast for the earthquake-generating zone of the Kuril-Kamchatka arc for the next five years, April 2008 to March 2013. Explanations are given for the method of calculation and prediction. The probable locations of future M ≥ 7.7 earthquakes are specified. For all segments of the earthquake-generating zone we predict the expected phases of the seismic cycle, the rate of low-magnitude seismicity (A10), the magnitudes of moderate-sized earthquakes to be expected, with probabilities of 0.8, 0.5, and 0.15, their maximum possible magnitudes, and the probabilities of occurrence of great (M ≥ 7.7) earthquakes. The results of these forecasts are used to enhance seismic safety.  相似文献   

18.
We analyze the ground motion time histories due to the local seismicity near the Itoiz reservoir to estimate the near-source, surface 3D displacement gradients and dynamic deformations. The seismic data were obtained by a semipermanent broadband and accelerometric network located on surface and at underground sites. The dynamic deformation field was calculated by two different methodologies: first, by the seismo-geodetic method using the data from a three-station microarray located close to the dam, and second, by single station estimates of the displacement gradients. The dynamic deformations obtained from both methods were compared and analyzed in the context of the local free-field effects. The shallow 1D velocity structure was estimated from the seismic data by modeling the body wave travel times. Time histories obtained from both methods result quite similar in the time window of body wave arrivals. The strain misfits between methods vary from 1.4 to 35.0 % and rotational misfits vary from 2.5 to 36.0 %. Amplitudes of displacement gradients vary in the range of 10?8 to 10?7 strains. From these results, a new scaling analysis by numerical modeling is proposed in order to estimate the peak dynamic deformations for different magnitudes, up to the expected maximum M w in the region (M5.5). Peak dynamic deformations due to local M w5.5 earthquakes would reach amplitudes of 10?5 strain and 10?3 radians at the Itoiz dam. The single station method shows to be an adequate option for the analysis of local seismicity, where few three-component stations are available. The results obtained here could help to extend the applicability of these methodologies to other sites of engineering interest.  相似文献   

19.
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20.
Clustering the epicenters of Caucasian earthquakes with magnitudes M ≥ 3.0 is carried out, and the epicentral zones of the probable earthquakes with M ≥ 5.0 areas where epicenters of earthquakes with M ≤ 5.0 may occur are recognized by the Fuzzy Clustering and Zoning (FCAZ) algorithmic system developed by the authors at the Geophysical Center of the Russian Academy of Sciences. These zones correspond well to the locations of the epicenters of earthquakes with M ≥ 5.0. The zones recognized in this study are compared with the zones previously recognized by A.D. Gvishiani et al. in 1988 by the Earthquake-Prone Areas Recognition (EPA) technique. The comparison shows that the zones identified by FCAZ are mainly located inside the EPA-zones. The FCAZ-zones are also compared with the zones previously recognized using gravimetric and geological data. The results obtained by different methods closely agree. Contrary to EPA technique FCAZ algorithmic system relies on the DPS algorithm of objective classification that requires only the information about epicenters of the earthquakes in the region under study.  相似文献   

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