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1.
Seismicity changes associated with reservoir loading   总被引：12，自引：0，他引：12  
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.
Pressure variations in a magma reservoir may cause deformation at the surface and a redistribution of the stress in the surrounding rock. In this study, we use two‐dimensional numerical models and elaborate how magma chamber inflation and deflation affect the stress field around and surface displacement. We test how a pre‐existing normal fault near the magma reservoir may influence the pattern of stress. We demonstrate the possibility of initiating both normal and reverse slip on faults during the inflation of the magma reservoir. The Coulomb failure stress changes are calculated during the periods of pressure variation. An increase of Coulomb failure stress can be predicted above and below the magma chamber during increasing magma chamber pressure that may encourage earthquakes. This process can produce cracks and fault growth encouraging magma propagation along the cracked zone. A different distribution of the stress change is expected in the case of subsequent deflation of the overpressured magma reservoir. In this case, seismicity is expected on a plane at equal depth than the magma chamber, laterally offset from the extent of the magma chamber. Magma could propagate laterally from the magma reservoir into zones where cracks have been generated, but only if the resolved shear stress on the fault is small compared with the excess magma pressure.  相似文献   

3.
The Koyna region located in the west coast of India is a classic example of reservoir triggered seismicity (RTS) that started soon after the impoundment of the Koyna reservoir in 1962. Previous studies have shown that RTS can be explained in terms of stress and pore pressure changes due to poroelastic response of the rock matrix. The permeability of rock matrix is a key parameter for pore pressure diffusion which is mainly responsible for generation of stress perturbation related to seismicity. Based on the poroelastic theory, we employ 2-D finite element models to simulate the evolution of pore pressure up to 5 years after the reservoir impoundment in 1962, using a range in permeability, 10?16–10?14 m2. Constraints on material properties of Deccan basalt and granitic rocks were taken from available studies. The results show the formation of pore pressure front and its propagation with depth and time since the reservoir impoundment as a function of permeability. While a permeability of 10?16 m2 does not produce any significant change in pore pressure, a ten-fold increase in permeability produces significant changes up to a depth of 2 km only beneath the reservoir after 5 years of impoundment. Permeability values between 10?15 m2 and 10?14 m2 are required to induce critical pore pressure changes in the range 0.1–1 MPa up to depth of 10 km, capable of triggering earthquakes in a critically stressed region. Studies on core samples of granitic basement rock down to a depth of 1522 m in the Koyna region provide evidences of fracture zones that may contribute to water channelization. Direct measurements of material properties through the ongoing deep drilling programme would help to develop more realistic models of RTS.  相似文献   

4.
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 × 109 m3. 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   

5.
The status of Reservoir Induced Seismicity (RIS) has been reviewed periodically (Rothé, 1968, 1973; Gupta and Rastogi, 1976; Simpson, 1976; Packer et al., 1979). In the present paper, the significant work carried out during the last three years on RIS is reviewed.An earthquake of magnitude occurred on November 14, 1981 in the vicinity of Aswan Lake, Egypt, 17 years after the filling started in 1964. This event occurred 4 days after the seasonal maximum in the reservoir water level and was followed by a long sequence of aftershocks. Another event of magnitude occurred in the vicinity of Aswan Lake on August 20, 1982. Results of preliminary investigations indicate that this seismic activity is reservoir induced. Recent analyses of induced seismic events at Nurek Reservoir U.S.S.R., show that the second stage of filling during August to December 1976, increasing the maximum depth from 120 m to 200 m, was accompanied by an intense burst of shallow seismic activity. An outward migration from the centre of the reservoir, possibly associated with diffusion of pore pressure, is revealed by the temporal distribution of earthquake foci. A variety of investigations including the in situ measurement of tectonic stress, pore pressure, permeability, distribution of faults, etc., in addition to monitoring seismicity, have been undertaken in the vicinity of the Monticello Reservoir, South Carolina. The largest reservoir induced earthquake is predicted not to exceed magnitude 5.The Koyna Reservoir, India, continues to be the most outstanding example of RIS. Three earthquakes of magnitude 5 occurred in September 1980. Earthquakes of magnitude 4 occur frequently in the vicinity of Koyna, the latest being on February 5, 1983. Events that occurred during the period 1967–1973 have been relocated using better procedures and are found to be much shallower and the epicentres less diffused. Location of 12 earthquakes of Ms 4.0, their foreshocks and aftershocks, that occurred during 1973–1976, composite focal mechanism solutions and related studies are consistent with the delineation of a N-S trending fault through the reservoir area. In a couple of interesting studies it has been demonstrated that earthquakes of magnitude 5.0 in the Koyna region are usually preceded by several magnitude 4 earthquakes in the preceding fortnight. Also, a rate of loading of Koyna reservoir of at least 40 ft/week appears to be a necessary, although not sufficient, condition for the occurrence of magnitude 5 earthquakes. Smooth filling/emptying appears to be the key to reduce the hazard of RIS.A map and a table of the reported cases of reservoir induced changes in seismicity through 1982 have been compiled.  相似文献   

6.
An earthquake of Mw 5.1 occurred on March 14, 2005, in the seismically active Koyna–Warna region in western India, the site known for the largest reservoir triggered seismicity (RTS) in the world. For more than four decades, earthquakes with M  4.0 have occurred in this region at regular intervals. Impoundment of reservoirs and changes in lake levels can trigger earthquakes by two processes of stress modifications, namely direct loading effect of the reservoir and diffusion through various faults and fractures. In this paper we analysed the reservoir water level data at Koyna and Warna reservoirs prior to the occurrence of the March 14, 2005 earthquake, to explain the dominant mechanism behind its occurrence and its correlation with the observed coseismic changes. We conclude that the diffusion process, not the reservoir load effect, is the dominating mechanism triggering earthquakes in the region. The coseismic changes in deep well water levels sensitive to earth tides are found to be to the order of 1–12 cm.  相似文献   

7.
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   

8.
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   


9.
Latian dam is located in the North East of Tehran in Elburz Mountain. It falls in the category of large dams according to the International Committee on Large Dams (ICOLD). It was constructed in 1967 for agricultural purposes, drinking water, and power generation. Producing triggered earthquakes may be a consequent result of dam construction. In this paper, the complete seismic statistics of the region from 1996 onwards has been studied to understand the seismic condition of Latain region. For this purpose, frequency of earthquakes within a radius of 30/60 km around the dam is studied considering its relationship with the reservoir volume variation. Using Gutenberg-Richter rule, parameter b of the region was determined within the same region. The results of this study show the existence of triggered seismicity around the reservoir of Latian dam. Considering the tectonic-geological condition of the region, the existence of triggered earthquakes may create landslides in the reservoir and around it.  相似文献   

10.
We present the results of the first airborne LiDAR survey flown in the Koyna-Warna region and examine the relationship between the lineament fabric and the ongoing seismicity in the region. Our studies reveal that earthquakes of M≥4.0 for the period 1968 to 2016 are strongly correlated with a 10 km wide N-S fracture zone, which not only represents the surface expression of seismically active basement faults, but also act as conduits for water percolation between the Koyna and Warna reservoirs. A decreasing trend in the annual distribution of earthquakes was observed from 1985. A new burst of seismic activity in 1993 followed the impoudment of the Warna reservoir. We report a change in annual seismicity pattern, where seismicity peaks during September and December in the pre-Warna period, with a new peak emerging during March-April subsequent to the impoundment of Warna reservoir. A model is proposed to explain the seismicity along dominant N-S lineaments and the impact of Warna reservoir impounding which altered the hydrogeologic regime in the region.  相似文献   

11.
Consolidation theory and concepts of rock failure can be used to evaluate the probable risk of induced seismicity as a result of filling of reservoirs. This evaluation indicates the safest way to fill a reservoir, and depends only on the geometry of the load, the rate of filling and the geological structures in the area. The stability function is actually a measure of the risk of having failure, with time, for a particular loading history in respect to a plane of weakness.

The stability function is applied to the area of the Itzantun reservoir, which will be in southern Mexico. Drawdowns can increase the risk of triggering earthquakes in this area, which is prone to thrust faulting. It is possible to estimate the stresses after a period during which the water level is maintained and a decrease in stresses with the depth of the observation point.

The estimates of the probable induced seismicity are limited as the residual stress in the area prior to the impounding is unknown. With a measure of the residual tectonic stress it will be possible to determine an optimal filling rate to reduce the probability of induced seismicity.  相似文献   


12.
We use a continuum model of reservoir evolution to explore the interaction of coupled thermal, hydraulic and chemical processes that influence the evolution of seismicity within a fractured reservoir from stimulation to production. Events occur from energy release on seeded fractures enabling moment magnitude, frequency and spatial distribution to be determined with time. Event magnitudes vary in the range ?2 to +2 with the largest event size (~2) corresponding to the largest fracture size (~500 m) and a prescribed stress drop of 9 MPa. Modelled b‐values (~0.6–0.7) also correspond to observations (~0.7–0.8) for response in the Cooper Basin (Australia). We track the hydrodynamic and thermal fronts to define causality in the triggering of seismicity. The hydrodynamic front moves twice as fast as the thermal front and envelops the triggered seismicity at early time (days to month) – with higher flow rates correlating with larger magnitude events. For later time (month to years), thermal drawdown and potentially chemical influences principally trigger the seismicity, but result in a reduction in both the number of events and their magnitudes.  相似文献   

13.
The deep seismicity of the Tyrrhenian Sea is analysed using data from a new instrumental catalogue of the seismicity of the Italian area. We use algorithms for the determination of absolute and relative hypocentral locations and for the evaluation of the geometry and coherence of the state of stress within the subducting slab. The structure of the Benioff zone, although simpler than previously indicated, reveals anomalous traits both in the seismicity distribution and in the stress geometry, confirming that standard subduction models cannot be applied in the Tyrrhenian region. The velocity anomaly and the location of few isolated events indicate that the subducted slabs extend to the north along the Apenninic chain approximately to the latitude of the Irpinia region, in Central Italy (? 42°N).  相似文献   

14.
Earthquakes in Koyna-Warna region are triggered by the reservoirs but the reasons for sustained seismicity, in terms of magnitude and time, remain enigmatic. We critically review the proposed models/processes, which include fault interaction, flexure of Western Ghat escarpment, velocity heterogeneity, and earthquakes being considered as aftershocks. We suggest that each of these processes or models have limitations and are not capable of explaining all the features of seismicity individually. It is possible that all put together and some other unknown additional processes are at work and there is a mish-mash of several processes attending the region, causing continuing seismicity for past five decades.  相似文献   

15.
水库蓄水对库岸滑坡的影响研究   总被引：6，自引：1，他引：5  
王明华  晏鄂川 《岩土力学》2007,28(12):2722-2725
水库蓄水将显著改变库岸的水文地质条件,进而影响滑坡的稳定状态。以鄂西南某水库为例,阐述了库水位对滑坡稳定性影响的一般规律,并采用剩余推力法计算分析了滑带土抗剪参数、库水位变化和地下水疏干系数对库岸滑坡的影响。在此基础上,对蓄水后库岸滑坡的变形模式进行了模拟分析。研究表明,水库蓄水不仅使滑坡稳定性发生变化,滑坡的变形模式也将由推移式转变为牵引式。  相似文献   

16.
On 10th December 1967, the world’s largest reservoir triggered seismic (RTS) event of magnitude 6.3 shook the Koyna region, the prime site of RTS globally. Ever since, several studies have attempted to infer the seismotectonics and to comprehend the actual causative mechanism of triggered seismicity in this region. Initial studies, including those of the 1967 Koyna main shock and its aftershocks, were based on the conventional P wave polarity or the first motion approach. These studies provided the first ever understanding of a predominantly strike-slip environment in the Koyna region, concurrent with the direction of ambient stress field due to the Indian plate motion. Subsequent studies pointed to a normal faulting environment in theWarna region further south, subsequent to impoundment later in 1985. A few studies did report solutions based on composite focal mechanisms, which however, only represent the average picture of the region. More recent studies based on modelling of seismic broadband waveform data provided more accurate focal mechanisms with unprecedented location accuracies including focal depths. A catalog of 50 focal mechanism solutions is now available for the earthquakes of magnitude ～4 and larger that occurred during the last 50 years, which has paved way for a clear understanding of the stress field and the causative model of seismogenesis in this active intra-plate seismic RTS zone in western India. Based on stress inversion using this catalog, a new tectonic model depicting a periodically varying stress field and hence faulting mechanism has been inferred.  相似文献   

17.
随着页岩气开采、废水回注和CO2地质封存工程活动的进行,储层应力环境改变诱发地震的问题得到广泛关注,研究储层岩石变形破裂和声发射规律对于理解诱发地震活动具有重要意义。本文选取了页岩、致密砂岩和白云岩开展三轴压缩声发射试验,获取了空间裂缝形态,揭示了不同类型储层岩石的变形破裂过程和声发射特征。结果表明：(1)页岩的扩容应力与峰值应力比最高,其次为白云岩和致密砂岩,表明页岩主要发生脆性破坏。(2)岩石结构对裂缝扩展和强度具有明显影响,页岩层理发育,抗压强度和裂缝形态各向异性显著。当层理角度为0°时,试样发生剪切-拉张复合型破坏。当层理角度为30°和60°时,试样主要发生剪切破坏。当层理角度增大至90°时,试样主要发生拉张破坏。致密砂岩破裂形成剪切主裂缝,白云岩形成两条剪切主裂缝和微裂缝。(3)不同类型储层岩石破裂过程声发射特征差异显著。页岩在扩容应力点附近有少量声发射活动,达到峰值应力时,声发射活动迅速增强。致密砂岩仅在破裂瞬间有少量声发射活动。相比之下,白云岩在裂缝非稳定扩展阶段和峰后阶段声发射活动显著。因此,在工程实践中需要根据微震监测调整施工措施,避免页岩作为储...  相似文献   

18.
Quantification of seismic activity is one of the most challenging problems faced by earthquake engineers in probabilistic seismic hazard analysis. Currently, this problem has been attempted using empirical approaches which are based on the regional earthquake recurrence relations from the available earthquake catalogue. However, at a specified site of engineering interest, these empirical models are associated with large number of uncertainties due to lack of sufficient data. Due to these uncertainties, engineers need to develop mechanistic models to quantify seismic activity. A wide range of techniques for modeling continental plates provides useful insights on the mechanics of plates and their seismic activity. Among the different continental plates, the Indian plate experiences diffused seismicity. In India, although Himalaya is regarded as a plate boundary and active region, the seismicity database indicates that there are other regions in the Indian shield reporting sporadic seismic activity. It is expected that mechanistic models of Indian plate, based on finite element method, simulate stress fields that quantify the seismic potential of active regions in India. This article explores the development of a finite element model for Indian plate by observing the simulated stress field for various boundary conditions, geological and rheological conditions. The study observes that the magnitude and direction of stresses in the plate is sensitive to these conditions. The numerical analysis of the models shows that the simulated stress field represents the active seismic zones in India.  相似文献   

19.
The Mw7.5 Palu earthquake that occurred on September 28, 2018, in Indonesia caused much damage to the city of Palu. Preliminary investigations indicated that the Palu‐Koro Fault (PKF) hosted this damaging event. We calculated the seismicity before and after the 1996 Minahasa Mw7.9 earthquake and found that the seismicity on the PKF was enhanced after this earthquake. The earlier earthquake added Coulomb stress changes (?CFS) to the seismogenic fault plane. We calculated the ?CFS produced by the Palu earthquake on a specified received nodal plane; the results suggest that many aftershocks occurred in the region of increased ?CFS. This region was consistent with the region of increased seismicity. The ?CFS on neighbouring faults increased, and up to 55.282 bar of stress was observed on the PKF. Furthermore, we calculated the expected seismicity rate and found that it will require ~50 years to recover to its original level.  相似文献   

20.
This paper examines the variability of seismic activity observed in the case of different geological zones of peninsular India (10°N–26°N; 68°E–90°E) based on earthquake catalog between the period 1842 and 2002 and estimates earthquake hazard for the region. With compilation of earthquake catalog in terms of moment magnitude and establishing broad completeness criteria, we derive the seismicity parameters for each geologic zone of peninsular India using maximum likelihood procedure. The estimated parameters provide the basis for understanding the historical seismicity associated with different geological zones of peninsular India and also provide important inputs for future seismic hazard estimation studies in the region. Based on present investigation, it is clear that earthquake recurrence activity in various geologic zones of peninsular India is distinct and varies considerably between its cratonic and rifting zones. The study identifies the likely hazards due to the possibility of moderate to large earthquakes in peninsular India and also presents the influence of spatial rate variation in the seismic activity of this region. This paper presents the influence of source zone characterization and recurrence rate variation pattern on the maximum earthquake magnitude estimation. The results presented in the paper provide a useful basis for probabilistic seismic hazard studies and microzonation studies in peninsular India.  相似文献   

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