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  • Induced seismicity  (7)
  • 1995-1999  (7)
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  • 1
    ISSN: 1420-9136
    Keywords: Induced seismicity ; stress determination ; stress heterogeneity ; fluid flow ; fault morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The focal mechanisms of some one hundred microseismic events induced by various water injections have been determined. Within the same depth interval, numerous stress measurements have been conducted with the HTPF method. When inverted simultaneously, the HTPF data and the focal plane solutions help determine the complete stress field in a fairly large volume of rock (about 15×106 m3). These results demonstrate that hydraulically conductive fault zones are associated with local stress heterogeneities. Some of these stress heterogeneities correspond to local stress concentrations with principal stress magnitudes much larger than those of the regional stress field. They preclude the determination of the regional stress field from the sole inversion of focal mechanisms. In addition to determining the regional stress field, the integrated inversion of focal mechanisms and HTPF data help identify the fault plane for each for each of the focal mechanisms. These slip motions have been demonstrated to be consistent with Terzaghi's effective stress principle and a Coulomb friction law with a friction coefficient ranging from 0.65 to 0.9. This has been used for mapping the pore pressure in the rock mass. This mapping shows that induced seismicity does not outline zones of high flow rate but only zones of high pore pressure. For one fault zone where no significant flow has been observed, the local pore pressure has been found to be larger than the regional minimum principal stress but no hydraulic fracturing has been detected there.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1420-9136
    Keywords: Induced seismicity ; b-value statistics ; Ostrava-Karviná Coal Mine District
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The values of parameters of the relation logN=a−b logE characterize in general the level of seismicity of individual regions. In the present paper, a detailed analysis ofb values of the frequency-energy distributions was carried out with the aid of a database of seismic events recorded by the seismological networks in the Ostrava-Karviná Coal Mine District (Czech Republic), using the least squares regression and maximum likelihood method, as well. The determination ofb value was performed for a relatively large number of regions investigated and for different time series of observations. Special attention has been paid to induced seismic events statistics for the vicinity of one of the coalfaces in the Lazy Mine. It could be generally stated that lowerb values correspond to a higher level of induced seismic activity, while the higher ones correspond to a low and a moderate seismic activity.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 147 (1996), S. 277-288 
    ISSN: 1420-9136
    Keywords: Induced seismicity ; clustering ; space-time interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Elementary cluster analysis of induced seismicity in a South African gold mine has shown that there is a clear interaction amongst the clusters; and that the level of the interaction is a function of the distance. The clusering algorithm used is an adaptation of the single-link cluster analysis which considers both three-dimensional space and time. A high level of interaction between the clusters is demonstrated from the cross-correlation analysis of seismic activity rates and radiated energy. A distinct decrease in the value of correlation coefficients was detectable as distance increased. This was somewhat surprising, considering the simplicity of the technique used. Since no attempt is made to study the physical mechanisms of interaction, these results are very preliminary, but interesting from an observational point of view.
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  • 4
    ISSN: 1420-9136
    Keywords: Induced seismicity ; kinetics ; rock fracture ; rockburst ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Powerful seismic events, such as earthquakes and rockbursts, are caused by the accumulation of energy in rocks and loss of rock mass stability. Usually methods of their forecasting are based on the registration of anomalous behavior of geophysical fields. However an efficiency of this approach is low. The present paper proposes a kinetic approach to the description of rock fracture process, which can be used for the forecasting of seismic events and an investigation of structure and energy distributions in rock. 3-D and 1-D kinetic equations describing a process of cluster formation in rock were obtained. The equations are invariant to deformation conditions and to the scale level of events. They showed a good agreement with the results of field observations and laboratory experiments. It was also shown that these equations well describe the processes of earthquake, rockburst and rock sample failure preparation. Catalogues of rockbursts in mines were analyzed with the use of the kinetic equations to find out evidence of induced seismic events. The proposed approach makes it possible to reveal trends in rock behavior and thus predict the rock failure at different scale levels.
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  • 5
    ISSN: 1420-9136
    Keywords: Induced seismicity ; gas field ; seismic deformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract With objective of investigating the peculiarities of seismic process development and seismotectonic deformation character in the focal area of the Gazli earthquakes of 1976 (7.0〈M〈7.3) and 1984 (M=7.2), a local seismic network was installed. For the field observation period (May to June, 1991) more than 400 events with magnitudes −0.2〈M〈4.5 were recorded by at least 6 stations. Isometric presentation of earthquake hypocenters distribution allows us to define the depth and dipping planes orientation of seismoactive faults of the region. The focal mechanisms of 35 earthquakes for the period 1979–1988,M〉2.8, connected to a gas extraction regime period, and 75 events 1〈M〈4.3 for the 1991 period (gas storage regime) are used to analyze the dynamics of seismotectonic deformation processes (SDP) in this region. It has been ascertained, that the earth's crust in the Gazli region is subject to complicated deformation processes, particularly below 4 km depth. The predominant kind of deformation is compression. Vertical velocities of deformation show uplift of most of the region during the period of field work. The maximum velocity of vertical deformations for the Gazli structure isV=0.41 mm/year. The comparison of the vertical velocities' displacements due to seismic flow with recent tectonic movements of the earth's crust has revealed their direct relation and high percentage of seismic flow contribution to the tectonic movement. The results obtained testify that the active seismic processes in the Gazli region are connected not as much as the residual stress release in the focal zone of the earthquakes 05. 1976 and 1984,M〉7.0 but rather with the influence of the gas reservoir exploitational regime on the rocks with different rheologic properties.
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  • 6
    ISSN: 1420-9136
    Keywords: Induced seismicity ; lake-level ; seismicity pattern ; pore pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Relation between water level changes and pattern of seismicity is an important consideration in studies of Reservoir Induced Seismicity (RIS). Sensitivity of the Regions around Lake Jocassee to small fluctuations in the lake level is presented in this paper. The seismic source regions in the area around the lake seem to be sensitive to changes in the lake level as small as 1 to 1.5 m. Although such changes may produce stress changes of the order of only 0.1 bar, their influence on the spatial pattern of earthquakes seems to be quite perceptible. Observations of this type may help understand the threshold values of pore pressure/effective stress changes that can activate fault zones under high fluid pressure.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 144 (1995), S. 191-209 
    ISSN: 1420-9136
    Keywords: Induced seismicity ; scaling relations ; self-similar behavior ; P- andS-wave corner frequencies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The values of seismic moment andS-wave corner frequency from 1575 seismic events induced in South African, Canadian, Polish, and German underground mines were collected to study their scaling relations. The values ofP-wave corner frequency from 649 events were also available. Seismic moments of these events range from 5*103 to 2*1015 N·m (moment magnitude is from −3.6 to 4.1), theS-wave corner frequency ranges from 0.7 to 4438 Hz, and theP-wave corner frequency is between 5 and 4010 Hz. The slope of a regression line between the logarithm ofS- andP-wave corner frequencies is equal to one, and the corner frequencies ofP waves are higher than those ofS waves on the average by about 25 percent. In studies of large and moderate earthquakes it has been found that stress drop is approximately independent of the seismic moment, which means that seismic moment is inversely proportional to the third power of corner frequency. Such a behavior was confirmed for most of the data considered here. A breakdown in the similarity betwen large and small events seems to occur for the events with moment magnitude below −2.5. The average values of seismic moment referred to the same range of corner frequency, however, are vastly different in various mining areas.
    Type of Medium: Electronic Resource
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