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1.
Changes in seismic activity have been related to the filling of large reservoirs in over thirty cases. These changes range from variations in the level of micro-earthquake activity detectable only with instruments of high sensitivity to destructive earthquakes with magnitudes greater than 6. On the other hand, the filling of many other large reservoirs has not been accompanied by increased seismicity. A number of factors may contribute to the generation or absence of post-impounding seismicity. Increased vertical stress due to the load of the reservoir and decreased effective stress due to increased pore pressure can modify the stress regime in the reservoir region. Whether or not these stress changes are sufficient to generate earthquake activity will depend on a complex interaction of the induced stress with the state of pre-existing stress near the reservoir, and on the geologic and hydrologic conditions at the site. The combined effect of increased vertical load and increased pore pressure will have the greatest tendency to increase activity in regions where the maximum compressive stress is vertical (normal faulting). In regions where the minimum compressive stress is vertical (thrust faulting) increased stress due to a vertical load should have a minimum effect. For all of the larger reservoir-induced earthquakes the stress system determined from fault plane solutions is in agreement with the pre-existing stress field in the region of the reservoir. These earthquakes are all of strike-slip or normal type, there being no reported cases of large induced earthquakes with thrusting mechanisms. The potential for major changes in seismicity may be highest in regions of moderate strain accumulation (low to moderate natural seismicity). In areas of high strain accumulation and high levels of natural seismicity, the stress changes induced by the reservoir will be small compared to natural variations. In aseismic areas, with low strain accumulation, the reservoir-induced stresses may be insufficient to raise the stress level to a state of failure. 相似文献
2.
More than 30 cases of seismicity associated with dam reservoir sites are known throughout the world. Despite the lack of data
in some areas, where seismicity occurred after reservoir impounding, there have been distinct seismic patterns observed in
seismic areas after dam projects implantation. This has demonstrated that reservoir loading can trigger earthquakes.
A mechanism of earthquake generation by reservoir impounding is proposed here with particular application to the Brazilian
cases and to areas subject to low confining stress conditions in stable regions. Six artificial lakes are described and the
associated earthquake sources are discussed in terms of natural or induced seismicity. Earthquake monitoring in Brazil up
to 1967, when Brasilia's seismological station started operation, was mainly based in personal communications to the media.
Therefore, there is a general lack of seismic records in relatively uninhabited areas, making it difficult to establish a
seismic risk classification for the territory and to distinguish natural from induced seismicity. Despite this, cases reported
here have shown an alteration of the original seismic stability in dam sites, after reservoir loading, as observed by the
inhabitants or records from Brasilia's seismological station. All cases appear to be related to an increase in pore pressure
in permeable rocks or fracture zones which are confined between impermeable rock slabs of more competent rock. It is apparent
that some cases show some participation of high residual stress conditions in the area. 相似文献
3.
Five seismic events occurred between August 1979 and May 1980 in the Belchatow trench area in central Poland, where large brown-coal deposits have been surface-mined since 1976. The three largest shocks had a local magnitude ML = 3.5 , seismic moment Mo = 1.5 · 10 14 N-m and source radius r = 350m , approximately. The tremors had maximum intensity between 5 and 6, and from the magnitude—intensity—depth relation, the focal depth was estimated to be between 1 and 5 km. The Belchatow tremors are the manifestation of an unusual type of induced seismicity, i.e., seismicity connected with surface mining. The removal of overburden and extensive ground-water withdrawal by the mining operations seem to be direct factors responsible for stress concentration, although preexisting tectonic stress might be the most important indirect factor responsible for the origin of these events. 相似文献
4.
We report here that seismicity near Govind Ballav Pant reservoir is strongly influenced by the reservoir operations. It is the second largest reservoir in India, which is built on Rihand river in the failed rift region of central India. Most of the earthquakes occurred during the high water stand in the reservoir with a time lag of about 1 month. We use the concept of coulomb stress change and use Green's function based approach to estimate stresses and pore pressure due to the reservoir load. We find that the reservoir increases coulomb stress on the nearby faults of the region that are favourably oriented for failure in predominantly reverse slip manner under the NNE–SSW compression and thus promotes failure. The above two factors make it an obvious, yet so far unreported case of reservoir triggered seismicity. 相似文献
5.
CO 2 capture and storage projects must consider the potential possibility ofinjection induced seismicity. Moderate earthquakes and strong earthquakes may endanger human life and property, and even felt earthquakes and microquakes also pose a threat to seal integrity of CO 2 reservoir and increase the risk of leakage. Underground fluid injection induced seismicity usually happens in some geoengineering projects such as waste fluid disposal, EOR and EGS, and it occurs when fluid is injected along the fault. Therefore, it can be studied through stress analysis. The density of supercritical CO 2 is smaller than water, which may develop density flow in the deep strata or water-rock interactions in pre-existing structures, and cause the variation in permeability and pressure to induce a seismic activity. In this paper, we reviewed the mechanism of underground fluid injection induced seismicity with the focus of CCS, combined with fluid injection projects and seismic monitoring analysis in both commercial scale and experimental scale, to investigate its impact on the integrity of the cap rock of the reservoir. Finally, we summarized the appropriate site selection, injection methods and monitoring programs to prevent the occurrence of induced seismicity. 相似文献
6.
Folds and faults in the Devonian shales of the Berea area, Ohio have been analyzed on a small scale (several meters) to determine their method of formation. A simple elastic model has been developed to account for stress concentration due to lithostatic pressures induced by local relief. This analytical model is then coupled to the beam–column buckling stability theory. The possibility of failure due to faulting is also examined using the Coulomb criterion. Initial results indicate that local stresses due to topography are a probable cause of these structures, though the possible role of regional tectonic effects cannot be eliminated. The state of the local stress field and the possibility of seismic events have important implications for surface and subsurface design problems. 相似文献
7.
The state of stress around cavities is heterogeneous. Consequently, the state of fracture may also vary from point to point. Under compressive loading, cavity may be in one of four possible states: pre-fracture (pre-microfracture initiation), microfracture propagation (initiation to the onset of dilata dilatancy to failure) and post-failure. These four states are separated by the crack initiation stress, the crack damage stress and the failure stress. fracture events with confining pressure is examined with reference to three intact rocks: a brittle granite, a semi-brittle limestone and a ductile sal The maximum principal stress (σ1) at crack initiation, crack damage (onset of dilatancy), yielding and failure are established as a function stress (σ3). For a single intact rock, all four fracture events can be represented using one function (the Rocker function) with a single fac various fracture states. The proposed fracture criteria, based on the experimental data, are combined with the existing state of stress to prepare a fracture map around an elli intact Lac du Bonnet granite. The state of stability is expressed through a newly defined stability factor, the unconfined strength ratio (USR), wh to the traditional safety factor. In contrast to the conventional safety factor in rock mechanics (SFstrength/σ1), which is σ3 3–σ1, space of the stability diagram. 相似文献
8.
In the region of Three Gorges Reservoir (TGR) in China, there has been occurrence of several frequent earthquakes of moderate intensity since reservoir impounding occurred in 2003. These earthquakes are generally believed to be induced by reservoir impoundment and water-level variations. Usually, the geo-stress will change, when natural earthquakes occur. Following this principle, this paper adopted the rate and state theory to simulate and estimate Coulomb stress changes in the TGR region and obtained the pattern of Coulomb stress changes with time and the event sequence as well as the distribution of Coulomb stress changes in space. First, the TGR regional catalogue was analyzed and processed, leading to quantification of the magnitude of completeness and all of the parameters that are used in the stress–seismicity inversion process, including the reference seismicity rates, characteristic relaxation time, fault constitutive parameters, and stress rates. Second, the temporal evolution of the stress changes in different time windows was computed and analyzed, and it was found that there is an association between the Coulomb stress changes and rates of increase in the cumulative number of earthquakes. In addition, the earthquake occurred in November 2008 ( M S = 4.1) was analyzed and attempted to simulate the distribution of stress changes in space through the stress–seismicity inversion model. The results proved that the modeled area coincides with the historical area of earthquakes that occurred after 2008. Finally, a prediction was made about the earthquake productivity rates after 2015, which showed a declining earthquake rate over time that ultimately returned to the background seismicity. This result is essentially in agreement with Omori’s law. To conclude, it is rational to use the stress-inversion method to analyze the relationship between induced earthquake seismicity and local stress changes as well as to simulate the area of earthquake occurrence and productivity rates of reservoir-induced earthquakes. 相似文献
9.
A probabilistic 3-D slope stability analysis model (PTDSSAM) is developed to evaluate the stability of embankment dams and their foundations under conditions of staged construction taking into consideration uncertainty, spatial variabilities and correlations of shear strength parameters, as well as the uncertainties in pore water pressure. The model has the following capabilities: (1) conducting undrained shear strength analysis (USA) and effective stress analysis (ESA) slope stability analysis of staged construction, (2) incorporation of field monitored data of pore water pressure, and (3) incorporation of increase of undrained shear strength with depth, effective stress, and pore water pressure dissipation. The PTDSSAM model is incorporated in a computer program that can analyze slopes located in multilayered deposits, considering the total slope width. The main outputs of the program are the geometric parameters of the most critical sliding surface (i.e., center of rotation/radius of rotation and critical width of failure), mean 2-D safety factor, mean 3-D safety factor, squared coefficient of variation of resisting moment, and the probability of slope failure. The program is applied to a case study, Karameh dam in Jordan. Monitored data of induced pore water pressure in the dam embankment and soft foundation were gathered during dam construction. The stability of Karameh dam embankment and foundation was evaluated during staged construction using deterministic and probabilistic analysis. Foundation stability was evaluated based on the monitored data of pore water pressure. The study showed that the mean values of the corrective factors which account for the discrepancies between the in situ and laboratory-measured values of soil properties and for the modeling errors have significant influence on the 2-D safety factor, 3-D safety factor, slope probability of failure, and on the expected failure width. The degree of spatial correlation associated with shear strength parameters within a soil deposit also influences the probability of slope failure and the expected failure width. This correlation is quantified by scale of fluctuation. It is found that a larger scale of fluctuation gives an increase in the probability of slope failure and a reduction in the critical failure width. 相似文献
10.
文章简介了下汤地区区域地质及地震地质条件,分析了下汤地区岩体渗透性、现代地应力场特征及车村—鲁山断裂现代活动性。从地质条件分析、工程地质地震地质类比、危险度估算及统计检验等诸方面,论证了下汤水库诱发地震的可能性;结合岩石断裂力学研究成果预测了下汤水库诱发地震的可能震级和震中位置。 相似文献
11.
Geomechanical simulations were conducted to study the effects of reservoir depletion on the stability of internal and boundary faults in gas reservoirs overlain by elastic and viscoelastic salt caprocks. The numerical models were of a disk-shaped gas reservoir with idealized geometry; they mimic the structure of a gas field in the northern Netherlands which has experienced induced seismicity during gas production. The geomechanical simulations identified the area of the internal fault most sensitive to fault reactivation as coinciding with the epicenters of the largest seismic events associated with gas production. Depletion-induced shear slip is initiated at the depth of the reservoir, in the fault areas where the vertical fault throw ranges between 0.5 and 1.5 times the reservoir thickness. The extent of reactivated area differs depending on whether the caprock is viscoelastic or elastic: when it is viscoelastic, there is more down-dip shear displacement. High initial horizontal stresses in the rock salt and lower stresses in the elastic side-seal and the reservoir promote unloading of the internal and reservoir-bounding faults even before the reservoir is depleted. Particularly prone to fault reactivation are the fault zones along the interface between the reservoir rock and the salt caprock, which may already be critically stressed before depletion and are likely to be reactivated early during gas production. Stress relaxation and associated geomechanical changes affecting fault stability and ground surface deformation may continue long after production has ceased, due to the viscous behavior of the salt. 相似文献
12.
The seismicity of Israel has been evaluated from documented earthquake records of the present century and two years of routine monitoring of microearthquake activity by means of eleven stations spreading from the Gulf of Elat to northern Galilee. The Dead Sea rift asserts itself as the tectonic feature that accounts for the seismicity of our region. The activity peaks at zones where the fault branches sideways or at a junction with other fault systems. In particular, the crescent fault of Wadi Faria seems to be a zone of high strain accumulation. This is probably the site of many historical earthquakes which caused inland and coastal damage. It is thus found that the most active fault today which constitutes the greatest seismic risk to Israeli metropolitan areas extends along the Dead Sea rift from 31.2°N to 33.4°N. The seismicity around the Dead Sea conforms with the proposed movement along en-echelon faults. While the southwest segment is presently inactive, most of the seismic activity there is limited to the neighbourhood of its eastern shore with extreme seismicity at its southern tip near the prehistorical site of Bab-a-Dara'a. The seismicity of the Arava is much lower than the Jordan-Dead Sea section. The seismicity of the Israeli coast was found to be somewhat higher than that of the Arava. 相似文献
13.
After the filling up of the Hsinfengkiang Reservoir Kwangtung Province, seismicity was greatly increased. The majority of earthquakes occurred in the deep water gorge close to the dam, concentrated within a northwest belt. They are usually of shallow focal depths. A strong earthquake with magnitude 6.1 took place on March 19, 1962, about two and a half years since the impounding of the reservoir. According to the results of analysis of data from geodetic leveling and the spectra of seismic waves, the fault parameters of the main shock were determined. The fault plane solutions of 150 small earthquakes, occurring within a period of 18 months before and after the main shock were determined from the amplitudes of the first motion of P wave. The directions of the earthquake generating stress of about 2000 small earthquakes were obtained by smoothing the first motion patterns. Displacement field and stress field in the rock bodies underneath the reservoir caused by the loading of the reservoir water were calculated. Variations of the velocity ratio of the P and S waves prior to the main shock and several strong aftershocks were analysed. In consideration of the seismicity as well as the geological background, we endeavour to discuss the cause of reservoir impounding earthquakes at Hsinfengkiang. We have the opinion that the penetration of water along fissures becomes the most important cause of the main shock of March 19, 1962 at Hsinfengkiang. 相似文献
14.
Microearthquake observations are used to study the local seismicity and seismotectonics in the Precambrian Rapakivi Granite, in the Loviisa area, SE Fi around the nuclear power plant in Loviisa, is limited to a radius of 100 km. The results from a local microearthquake network in the Loviisa area showed that, during 6 years of measuring there were 29 micro- and ultra-microearth 0.1–1.2) in the area. The events identify active faults in the area. The estimated value of the peak slip is an important parameter connecting microearthquakes to geodynamical processes. The peak slip gives an approximat and aseismic movement on a certain fault and thus an indication of ongoing tectonic processes. The movements on the active fault may continue for thous Source parameters were computed for a simple circular source model, giving peak slips less than 0.25 mm, stress drop values less than 2 × 105N/m2 and source radii generally less than 50 m. The earthquakes occurred at depths of less than 5 km. 相似文献
15.
Theories of the physical processes leading to the stimulation of seismic activity by underground explosions, fluid injection, and reservoir impoundment are summarized. In all cases, the materials must be pre-stressed to a substantial fraction of their breaking strength in order for seismicity to be induced. Stress concentrations due to the presence of old faults or to inhomogeneities in the material properties play an important role in localizing induced seismicity. For the few cases for which data are available, the stimulation of earthquakes by fluid injection in bore holes is adequately explained by a Coulomb-Mohr failure criterion and the concept of effective pressure in a water-filled porous mechanism. Reservoir-related earthquakes are most likely due to the same mechanism, but, in view of the low injection pressures, additional physical or chemical effects of the water on the materials may play an important role. There may be a weakening of the materials in old fault zones by the introduction of water or static fatigue in silicate rocks due to stress corrosion. 相似文献
16.
The Castanhão reservoir was built in the state of Ceará, a dry region in Northeastern Brazil, to regulate the flow of the Jaguaribe River, for irrigation, and for power generation. It is an earth-filled dam, 60 m high, with a water capacity of 4.5 × 10 9 m 3. The seismicity in the area has been monitored since 1998, with a few interruptions, using one analog or one digital station and, during a few periods, a three-station network. The first earthquakes likely to be induced events were detected in 2003, when the water level was about 20 m high. In early 2004 a very heavy rainfall season quickly filled the reservoir. Shortly after, an increase in the seismic activity occurred and many micro-earthquakes were recorded. We suggest that this activity resulted from an increase in pore pressure due to undrained response. Therefore, we may classify this cluster of micro-earthquakes as “initial seismicity.” We deployed a network with four analog stations in the area, following this activity, to determine the epicentral zone. At least three epicentral areas under the reservoir were detected. The spatio-temporal analysis of the available data revealed that the seismicity occurs in clusters and that these were activated at different periods. We identified four sets of faults (N–S-, E–W-, NW–SE-, and NE–SW-oriented), some of which moved in shallow crustal levels and as recently as the Quaternary (1.8 Ma). Under the present-day stress regime, the last two sets moved as strike-slip structures. We suggest a possible correlation between dormant faults and the observed induced seismicity. 相似文献
17.
Correlations between time-dependent parameters of incremental stress and induced seismicity during the filling of Lake Kariba (Rhodesia/Zambia) support the hypothesis, originally advanced in 1970, that failure was at that time triggered by increment to the existing tectonic stress field. About three years after the mainshock of September, 1963, these correlations disappeared and it is suggested that the principal triggering mechanism has been increase of pressure in the water in pores and fractures of the rock, from mid-1966 through 1974. The Mohr failure criterion with Coulomb friction is used to show that both types of triggering are possible in a normal-fault régime. Triggering by incremental solid stress requires a friction coefficient < 0.577 in a normal-fault stress field. If the Okavango Delta, the Middle Zambezi Rift and the Luangwa Rift form a single member of the African Rift system, the only two flooded parts of this rift are now the main centres of seismic activity, namely the Okavango Delta and Lake Kariba. 相似文献
18.
Poro‐mechanical and thermo‐mechanical processes change the fracture aperture and thus affect the water flow pattern in the fracture during the cold water injection into enhanced geothermal systems (EGS). In addition, the stresses generated by these processes contribute to the phenomenon of reservoir seismicity. In this paper, we present a three‐dimensional (3D) partially coupled poro‐thermoelastic model to investigate the poroelastic and thermoelastic effects of cold water injection in EGS. In the model, the lubrication fluid flow and the convective heat transfer in the fracture are modeled by the finite element method, while the pore fluid diffusion and heat conductive transfer in the reservoir matrix are assumed to be 3D and modeled by the boundary integral equation method without the need to discretize the reservoir. The stresses at the fracture surface and in the reservoir matrix are obtained from the numerical model and can be used to assess the variation of in situ stress and induced seismicty with injection/extraction. Application of the model shows that rock cooling induces large tensile stresses and increases fracture conductivity, whereas the rock dilation caused by fluid leakoff decreases fracture aperture and increases compressive total stresses around the injection zone. However, increases in pore pressure reduce the effective stresses and can contribute to rock failure, fracture slip, and microseismic activity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
Failure mechanisms of the rock mass in the regions of maximum stress concentrations around a longwall face were assessed. In this respect, seismic events that result from changes in the stress field were analyzed to gain more knowledge about rock failure mechanisms in the proximity of the face area. A deep longwall mine developed at depths of about 3–3.5 km in South Africa was selected as a case study. Seismic moment tensor solutions were obtained for 32 seismic events with moment magnitudes in the range of 0.49 and 2.10. Through moment tensor decomposition, the dominant failure mechanisms were investigated by drawing focal mechanism plots. Further analysis was implemented by depicting the corresponding 3D radiation patterns of P-wave particle motions. Although the results cover various failure mechanisms, the dominant mechanisms are shear, implosional, and compressional failures. According to the results, most of the maximum principal stresses in the mine are compressive and oriented nearly vertical, which are in accordance with the gravitational collapses of the mined out areas. The results obtained from this research show that measuring and analyzing mining-induced seismicity can be a reliable measure to characterize the dominant failure mechanisms in a nondestructive manner and to provide a useful assessment of the stability of the longwall face in advance of extraction. 相似文献
20.
The association between fluid injection and seismicity has been well documented and widely publicized. Less well known, but probably equally widespread are faulting and shallow seismicity attributable solely to fluid extraction, particularly in association with petroleum production. Two unequivocable examples of seismicity and faulting associated with fluid extraction in the United States are: The Goose Creek, Texas oil field event of 1925 (involving surface rupture); and the Wilmington, California oil field events (involving subsurface rupture) of 1947, 1949, 1951 (2), 1955, and 1961. Six additional cases of intensity I–VII earthquakes (M < 4.6) without reported faulting may be attributable to shallow production from other large oil and gas fields. In addition to these examples are thirteen cases of apparently aseismic surface rupture associated with production from California and Texas oil fields. Small earthquakes in the Eloy—Picacho area of Arizona may be attributable to withdrawal of groundwater, but their relation to widespread fissuring is enigmatic. The clearest example of extraction-induced seismicity outside of North America is the 1951 series of earthquakes associated with gas production from the Po River delta near Caviga, Italy. Faulting and seismicity associated with fluid extraction are attributed to differential compaction at depth caused by reduction of reservoir fluid pressure and attendant increase in effective stress. Surface and subsurface measurements and theoretical and model studies show that differential compaction leads not only to differential subsidence and centripetally-directed horizontal displacements, but to changes in both vertical- and horizontal-strain regimes. Study of well-documented examples indicates that the occurrence and nature of faulting and seismicity associated with compaction are functions chiefly of: (1) the pre-exploitation strain regime, and (2) the magnitude of contractional horizontal strain centered over the compacting materials relative to that of the surrounding annulus of extensional horizontal strain. The examples cited include natural systems strained only by extraction of fluids, as well as some subsequently subjected to injection. Faulting and seismicity have accompanied both decrease and subsequent increase of fluid pressures; reversal of fluid-pressure decline by injection may enhance the likelihood of subsurface faulting and seismicity due chiefly to earlier fluid pressure reduction. A consistent common denominator appears to be continuing compaction at depth; the relative effects of fluid extraction followed by injection are not easily separated. 相似文献
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