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21.
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
22.
Izvestiya, Physics of the Solid Earth - Abstract—Based on the distribution of mantle seismicity and the sets of focal mechanisms of the earthquakes, the existence and deformation type of an... 相似文献
23.
On the Problem of Accounting for Paleoearthquakes When Evaluating the Seismic Hazard of Fennoscandia
Izvestiya, Atmospheric and Oceanic Physics - Earthquakes of magnitude M ≥ 6.5 have been unknown in Fennoscandia for almost 900 years of historical data, but a sharp outburst of postglacial... 相似文献
24.
Shevchenko V. I. Krupennikova I. S. Lukk A. A. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(10):1367-1380
Izvestiya, Atmospheric and Oceanic Physics - The neomobilist plate tectonic concept is currently at the forefront of geotectonics. This concept is based on the idea of the division of the... 相似文献
25.
The existence of a subvertical pillar-like cluster of earthquake hypocenters is established in the central part of the Garm geodynamic test area (Tajikistan). Seismotectonic deformation of the subvertical uniaxial extension prevails in the lower part of the cluster. This cluster is characterized by the absence of any relation to elements of the tectonic structure of the region. It is supposed that this element of the seismogenic structure of the region represents a channel of supply of deep fluids. Clusters of aftershock sources, close in morphology and position, are known in connection with the Altai, Neftegorsk, and Kultuk earthquakes. The subvertical but flattened-out in plan accumulations of aftershocks, unrelated to any elements of the tectonic structure of the Greater Caucasus, correspond to the Dagestan earthquake. Some other accumulations of earthquake hypocenters, so-called nests, such as the Vrancea and Hindu Kush ones, can be probably regarded as formations of a similar type. 相似文献
26.
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
27.
28.
A. V. Deshcherevskii K. M. Mirzoev A. A. Lukk 《Izvestiya Physics of the Solid Earth》2016,52(1):78-95
An advanced method for estimating the earthquake grouping parameters Rcr and Tcr is proposed in order to identify interrelated seismic events. The method pursues continuity with the previous algorithm suggested in (Mirzoev, 1980; 1988a; 1988b; 1992; Mirzoev and Azizova, 1983; 1984) but uses a more realistic spatial model of the background seismicity. All the calculations in the method can be fully formalized and a preliminary expert estimation of the parameters is not required. The method provides stable estimates of the critical radius Rcr and time Tcr of grouping. Group earthquakes make up 50 to 75% of their total number. 相似文献
29.
Izvestiya, Physics of the Solid Earth - Abstract—Statistical analysis of the focal mechanisms of the earthquakes based on the ISC standard catalog for 2001 to 2017 is carried out in the... 相似文献
30.
Shevchenko V. I. Lukk A. A. Guseva T. V. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(10):1488-1516
Izvestiya, Atmospheric and Oceanic Physics - The formation of fold–thrust dislocations of stratified rocks in the Earth’s crust has been considered as a consequence of the lateral... 相似文献