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Pradeep Talwani - One of the best experts on this subject based on the ideXlab platform.
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0033–4553:97:040511–40 $ 1.500.20:0 Seismotectonics of the Koyna-Warna Area, India
2016Co-Authors: Pradeep TalwaniAbstract:Abstract—Reservoir-Induced Seismicity has been observed near Koyna Dam, India since the early 1960s. In order to understand the seismotectonics of the region we analyzed available Seismicity data from 1963 to 1995. Over 300 earthquakes with M]3.0 were relocated using revised location parameters (station locations, velocity model, station delays and Vp:Vs ratio). The spatial pattern of earthquakes was integrated with available geological, geophysical, geomorphological data and observations following the M 6.3 earthquake in December 1967, to delineate and identify the geometry of seismogenic structures. From this integration we conclude that the area lying between Koyna and Warna Rivers can be divided into several seismogenic crustal blocks, underlain by a fluid-filled fracture zone. This zone lies between 6 and 13 km and is the location of the larger events (M]3.0). The Seismicity is bounded to the west by the Koyna River fault zone (KRFZ) which dips steeply to the west. KRFZ lies along the N–S portion of the Koyna River and extends S10°W for at least 40 km. It was the location of the 1967 Koyna earthquake. The Seismicity is bounded to the east by NE–SW trending Patan fault, which extends from Patan on the Koyna River, SW to near Ambole on the Warna River. Patan fault dips 45 ° to the NW and was the location of the M 5.4 earthquake in February 1994. The bounding KRFZ and Patan fault are intersected by several NW–SE fractures which extend from near surface to hypocentral depths. They form steep boundaries of the crustal blocks and provide conduits for fluid pressure flow to hypocentral depths. Sharp bends in the Koyna and Warna rivers (6 km south of Koyna Dam and near Sonarli, respectively) are locations of stress build-up and the observed Seismicity. Key words: Reservoir-Induced Seismicity—case history, seismotectonics, Koyna-Warna earth-quakes
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on the nature of reservoir induced Seismicity
International Conference on Multimedia Information Networking and Security, 1997Co-Authors: Pradeep TalwaniAbstract:—In most cases of Reservoir-Induced Seismicity, Seismicity follows the impoundment, large lake-level changes, or filling at a later time above the highest water level achieved until then. We classify this as initial Seismicity. This "initial Seismicity" is ascribable to the coupled poroelastic response of the reservoir to initial filling or water level changes. It is characterized by an increase in Seismicity above preimpoundment levels, large event(s), general stabilization and (usually) a lack of Seismicity beneath the deepest part of the reservoir, widespread Seismicity on the periphery, migrating outwards in one or more directions. With time, there is a decrease in both the number and magnitudes of earthquakes, with the Seismicity returning to preimpoundment levels. However, after several years some reservoirs continue to be active; whereas, there is no Seismicity at others. Preliminary results of two-dimensional (similar to those by Roeloffs, 1988) calculations suggest that, this "protracted Seismicity" depends on the frequency and amplitude of lake-level changes, reservoir dimensions and hydromechanical properties of the substratum. Strength changes show delays with respect to lake-level changes. Longer period water level changes (∼1 year) are more likely to cause deeper and larger earthquakes than short period water level changes. Earthquakes occur at reservoirs where the lake-level changes are comparable or a large fraction of the least depth of water. The Seismicity is likely to be more widespread and deeper for a larger reservoir than for a smaller one. The induced Seismicity is observed both beneath the deepest part of the reservoir and in the surrounding areas. The location of the Seismicity is governed by the nature of faulting below and near the reservoir.
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seismotectonics of the koyna warna area india
International Conference on Multimedia Information Networking and Security, 1997Co-Authors: Pradeep TalwaniAbstract:—Reservoir-Induced Seismicity has been observed near Koyna Dam, India since the early 1960s. In order to understand the seismotectonics of the region we analyzed available Seismicity data from 1963 to 1995. Over 300 earthquakes with M ≥ 3.0 were relocated using revised location parameters (station locations, velocity model, station delays and V p /V s ratio). The spatial pattern of earthquakes was integrated with available geological, geophysical, geomorphological data and observations following the M 6.3 earthquake in December 1967, to delineate and identify the geometry of seismogenic structures. From this integration we conclude that the area lying between Koyna and Warna Rivers can be divided into several seismogenic crustal blocks, underlain by a fluid-filled fracture zone. This zone lies between ∼6 and 13 km and is the location of the larger events (M ≥ 3.0). The Seismicity is bounded to the west by the Koyna River fault zone (KRFZ) which dips steeply to the west. KRFZ lies along the N–S portion of the Koyna River and extends S10°W for at least 40 km. It was the location of the 1967 Koyna earthquake. The Seismicity is bounded to the east by NE–SW trending Patan fault, which extends from Patan on the Koyna River, SW to near Ambole on the Warna River. Patan fault dips ∼45° to the NW and was the location of the M 5.4 earthquake in February 1994. The bounding KRFZ and Patan fault are intersected by several NW–SE fractures which extend from near surface to hypocentral depths. They form steep boundaries of the crustal blocks and provide conduits for fluid pressure flow to hypocentral depths. Sharp bends in the Koyna and Warna rivers (6 km south of Koyna Dam and near Sonarli, respectively) are locations of stress build-up and the observed Seismicity.
Joachim Peinke - One of the best experts on this subject based on the ideXlab platform.
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increase of order in seismic processes around large reservoir induced by water level periodic variation
Nonlinear Dynamics, 2008Co-Authors: Teimuraz Matcharashvili, Tamaz Chelidze, Joachim PeinkeAbstract:The importance of small periodic influences on the complex systems behavior is well acknowledged. In the present research, the possible impact of water level variation in large reservoir on the dynamics of local seismic activity was investigated. Large reservoirs located in the seismically active zones are often considered as a factor, quantitatively and qualitatively influencing earthquakes generation. During impoundment or after it, both the number and magnitude of earthquakes around reservoir significantly increases. After several years, these changes in earthquake generation, named as Reservoir-Induced Seismicity (RIS) essentially decrease down to the level, when lesser earthquakes occur with lower magnitudes. To explain this decrease, the authors of the present paper recently proposed the model of phase synchronization of local seismic activity by the periodic variation of the water level – Reservoir-Induced synchronization of Seismicity (RISS). Generally, RISS presumes a kind of control of local seismic activity by synchronizing small external periodic influence and hence increase of order in dynamics of regional seismic activity. To reveal these changes in dynamics of phase-synchronized seismic activity around large reservoir field, seismic and water level variation data were analyzed in the present work. Laboratory stick–slip acoustic emission data as a model of natural Seismicity were also analyzed. The evidence is presented that increase of order in dynamics of daily earthquake occurrence, earthquakes temporal, and energy distribution took place around Enguri high dam water reservoir (Western Georgia) during the periodic variation of the water level in the lake.
Stella Pytharouli - One of the best experts on this subject based on the ideXlab platform.
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interpretations of reservoir induced Seismicity may not always be valid the case of Seismicity during the impoundment of the kremasta dam greece 1965 1966
Bulletin of the Seismological Society of America, 2018Co-Authors: Stathis Stiros, Stella PytharouliAbstract:The ‘Kremasta seismic sequence’ in western Greece is one of the most commonly cited examples of Reservoir Induced Seismicity (RIS). Here, we show that this ‘sequence’ is a result of normal tectonic activity and that only some small, unrelated microseismic events are reservoir induced. Shortly after the beginning of the impoundment of the Kremasta Dam in 1965, the then newly established seismic monitoring network in Greece recorded two Ms ≥ 6.0 events and numerous small shocks spread over a 120 km wide region. These were interpreted as a single seismic sequence (namely the Kremasta seismic sequence), and assumed to be reservoir induced. We revisit the epicenter locations of these events and interpret them in the framework of the regional tectonic context and the local hydrogeology. Placing these events into the local context shows that they represent an amalgamation of separate, ordinary (tectonic) seismic sequences. Further, the regional rocks are highly fragmented by small faults and the spatial distribution of seismic events is not consistent with a model of stress transfer from reservoir loading. In addition, it is not likely that events at such long (> 20-30 km) distances from the reservoir could be induced by an initial reservoir load head of 30 m. Whilst the larger magnitude events are tectonic, after impoundment local residents reported an unusual frequency of small microseismic events felt only within 10 km of the dam. We provide evidence that these are a result of the collapse of numerous shallow karstic cavities adjacent and beneath the reservoir due to increased water load (locally 100-150 m depth). This study has significant implications for interpretation of seismic triggering mechanisms in other regions: earthquake occurrence within the proximity of reservoirs during and after impoundment time cannot be assumed to be RIS unless supported by seismological, geological and hydrogeological evidence.
Teimuraz Matcharashvili - One of the best experts on this subject based on the ideXlab platform.
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increase of order in seismic processes around large reservoir induced by water level periodic variation
Nonlinear Dynamics, 2008Co-Authors: Teimuraz Matcharashvili, Tamaz Chelidze, Joachim PeinkeAbstract:The importance of small periodic influences on the complex systems behavior is well acknowledged. In the present research, the possible impact of water level variation in large reservoir on the dynamics of local seismic activity was investigated. Large reservoirs located in the seismically active zones are often considered as a factor, quantitatively and qualitatively influencing earthquakes generation. During impoundment or after it, both the number and magnitude of earthquakes around reservoir significantly increases. After several years, these changes in earthquake generation, named as Reservoir-Induced Seismicity (RIS) essentially decrease down to the level, when lesser earthquakes occur with lower magnitudes. To explain this decrease, the authors of the present paper recently proposed the model of phase synchronization of local seismic activity by the periodic variation of the water level – Reservoir-Induced synchronization of Seismicity (RISS). Generally, RISS presumes a kind of control of local seismic activity by synchronizing small external periodic influence and hence increase of order in dynamics of regional seismic activity. To reveal these changes in dynamics of phase-synchronized seismic activity around large reservoir field, seismic and water level variation data were analyzed in the present work. Laboratory stick–slip acoustic emission data as a model of natural Seismicity were also analyzed. The evidence is presented that increase of order in dynamics of daily earthquake occurrence, earthquakes temporal, and energy distribution took place around Enguri high dam water reservoir (Western Georgia) during the periodic variation of the water level in the lake.
Stathis Stiros - One of the best experts on this subject based on the ideXlab platform.
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interpretations of reservoir induced Seismicity may not always be valid the case of Seismicity during the impoundment of the kremasta dam greece 1965 1966
Bulletin of the Seismological Society of America, 2018Co-Authors: Stathis Stiros, Stella PytharouliAbstract:The ‘Kremasta seismic sequence’ in western Greece is one of the most commonly cited examples of Reservoir Induced Seismicity (RIS). Here, we show that this ‘sequence’ is a result of normal tectonic activity and that only some small, unrelated microseismic events are reservoir induced. Shortly after the beginning of the impoundment of the Kremasta Dam in 1965, the then newly established seismic monitoring network in Greece recorded two Ms ≥ 6.0 events and numerous small shocks spread over a 120 km wide region. These were interpreted as a single seismic sequence (namely the Kremasta seismic sequence), and assumed to be reservoir induced. We revisit the epicenter locations of these events and interpret them in the framework of the regional tectonic context and the local hydrogeology. Placing these events into the local context shows that they represent an amalgamation of separate, ordinary (tectonic) seismic sequences. Further, the regional rocks are highly fragmented by small faults and the spatial distribution of seismic events is not consistent with a model of stress transfer from reservoir loading. In addition, it is not likely that events at such long (> 20-30 km) distances from the reservoir could be induced by an initial reservoir load head of 30 m. Whilst the larger magnitude events are tectonic, after impoundment local residents reported an unusual frequency of small microseismic events felt only within 10 km of the dam. We provide evidence that these are a result of the collapse of numerous shallow karstic cavities adjacent and beneath the reservoir due to increased water load (locally 100-150 m depth). This study has significant implications for interpretation of seismic triggering mechanisms in other regions: earthquake occurrence within the proximity of reservoirs during and after impoundment time cannot be assumed to be RIS unless supported by seismological, geological and hydrogeological evidence.