On the Dynamics of the Seasonal Components of Induced Seismicity in the Koyna–Warna Region, Western India (original) (raw)
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The behavior of seasonal variations in induced seismicity in the Koyna–Warna region, western India
Izvestiya, Physics of the Solid Earth, 2017
⎯Based on the earthquake catalog data for the Koyna-Warna region of induced seismicity in western India, the seasonal variations in seismic activity associated with annual fluctuations in the reservoir water level are analyzed over the time span of the entire history of seismological observations in this region. The regularities in the time changes in the structure of seasonal variations are revealed. The seasonal seismic activity is minimal in May-June when the reservoir level is lowest. During the remaining part of the year, the activity has three peaks: the fall peak in September, winter peak in November-December, and spring peak in February-March. The first mentioned peak, which falls in the phase of the water level reaching its maximal seasonal value is considered as the immediate response of the fluid saturated medium to the additional loading under the weight of reservoir water. The two subsequent maxima concur with the decline phase in the reservoir level and are interpreted as the delayed response associated with the changes in the properties of the medium due to water diffusion. It is shown that the intensities of the immediate and delayed responses to the seasonal water level variations both vary with time as does their ratio. The probable factors affecting the variations in the intensity of the seasonal components of the reservoir-induced seismicity are discussed.
Izvestiya, Physics of the Solid Earth, 2013
In 2000, the region of the Koyna-Warna water reservoirs in West India was hit by two strong earthquakes, which occurred six months apart and had magnitudes M > 5. The Koyna-Warna seismic zone is a typical region of induced seismicity with a pronounced correlation between seismicity and water level variations in the reservoirs. This indicates that the stress level in the region is close to critical; thus, insignifi cant variations in stress caused by the variations in the water level may trigger a strong earthquake. In order to study the preparatory processes in the sources of the induced earthquakes, in this paper we analyze the seismic catalogue for the Koyna-Warna region before a pair of strong earthquakes of 2000. The induced seismicity is found to exhibit prognostic variations, which are typical of preparation of tectonic earthquakes and indicative of the formation of metastable source zones of future earthquakes. Based on the obtained results, we suggest that initiation of failure in these metastable zones within the region of induced seismicity could have been caused by the external impacts associated with water level variations in the reservoirs and by the internal pro cesses of avalanche unstable crack propagation.
Journal of Asian Earth Sciences, 2015
Narsaiah, M., Naidu, S.M., Low deformation rate in the Koyna-Warna region, a reservoir triggered earthquake site in west-central stable India, Journal of Asian Earth Sciences (2014), doi: http://dx.Abstract We analyse nine years of GPS measurements of crustal deformation from the Koyna-Warna region within the stable India plate. The Koyna-Warna region experienced a strong earthquake on 10 December 1967 (M 6.3) that is considered to have been induced by the impoundment of the Koyna reservoir and the continuing earthquake activity in the region is considered to be associated with the Koyna and Warna reservoirs. The earthquakes occur in a very small region of 30×10 km 2 in two well defined seismic zones, the NNE-SSW trending Koyna Seismic zone, and the NNW-SSE trending Warna Seismic Zone. These zones are characterised by predominantly left-lateral strike slip motion and normal motion, respectively. In 2003, we initiated campaign-mode GPS measurements in the region.
Enhanced reservoir-induced earthquakes in Koyna region, India, during 1993–95
Journal of Seismology, 1997
Reservoir induced earthquakes began to occur in the vicinity of Shivajisagar Lake formed by Koyna Dam in Maharashtra state, western India, soon after its filling started in 1962. Induced earthquakes have continued to occur for the past 34 years in the vicinity of this reservoir, and so far a total of 10 earthquakes of M ≥ 5.0, over 100 of M ≥ 4 and about 100,000 of M ≥ 0.0 have occurred. Every year, following the rainy season, the water level in the reservoir rises and induced earthquakes occur. Seismic activity during 1967–68 was most intense when globally, the largest reservoir induced earthquake occurred on 10 December, 1967. Other years of intense seismic activity are 1973 and 1980. During 1986 another reservoir, Warna, some 20 km south of Koyna, began to be filled. The recent burst of seismic activity in Koyna-Warna region began in August, 1993, and was monitored with a close network of digital and analog seismographs. During August, 1993–December, 1995, 1,272 shocks of magnitude ≥ 2 were located, including two earthquakes of M 5.0 and M 5.4 on 8 December, 1993 and 1 February, 1994, respectively. Two parallel epicentral trends in NNE-SSW direction, one passing through Koyna and the other through Warna reservoir are delineated. The 1993 increase in seismicity has followed a loading of 44.15 m in Warna reservoir during 11 June 11, 1993 through August 4, 1993, with a maximum rate of filling being 16 m/week. The larger shocks have been found to be preceded by a precursory nucleation process.
Precursory changes in source parameters for the Koyna-Warna (India) earthquakes
Geophysical Journal International, 2004
Precursory changes of stress drop and corner frequency are found for five main earthquakes of M w 4.1 to 4.7 that occurred near the Koyna and Warna reservoirs during the period of our close monitoring from 1994 onwards. Earthquakes had started to occur in the area in 1962 soon after the impoundment of the Koyna reservoir and are still continuing. The epicentres are located in a 30-km-long, N-S seismic zone extending southwards from the Koyna dam. A new Warna reservoir, situated 25 km south of Koyna, was filled to 60 m in 1992. Most subsequent epicentres are close to the new Warna reservoir. Most M ≥ 4 earthquakes in this region have been associated with foreshocks for 15-30 days and aftershocks for over a month. At the beginning of various foreshock sequences of M w 1.5 to 2.4, the maximum stress drop values ranged from 0.25 to 0.65 MPa; the corner frequency ranged from 7.0 to 10.0 Hz for all the sequences. The stress drops decreased by over 50 per cent of their maximum value during the precursory period of 4-17 days prior to main shocks and remained at that low level for a few days after the main shocks. Following an initial increase, the corner frequency decreased by 8 to 45 per cent. The decrease in corner frequency implies a 9-54 per cent increase in fault length and is inferred to be caused by increased pore pressure as a result of dilatancy.
Temporal migration of earthquakes in KoynaWarna (India) region by pore-fluid diffusion
Journal of seismology, 2008
Continuous occurrences of several thousands of earthquakes in Koyna-Warna region since the initial impoundment (1962) of the Koyna reservoir has attracted the attention of seismologists all over the world to know the exact earthquake physical processes involved. The area has been a site for reservoir-triggered earthquakes for the last four and half decades.
Triggered and tectonic driven earthquakes in the Koyna– Warna region, western India
Two strong M>5.0 earthquakes within a span of six months occurred in a triggered seismicity environment in the Koyna-Warna region in western India in 2000. The region is experiencing continued seismicity since the last five decades indicating that this region is close to critical stresses and minor perturbations in the stresses due to reservoir loading and unloading can trigger earthquakes. In the present study we applied the technique developed for identification of prognostic anomalies for tectonic earthquakes to the Koyna-Warna catalogue prior to these two earthquakes with an aim to study the process of source preparation for triggered earthquakes. In case of tectonic earthquakes, unstable conditions in a source zone develop gradually leading to a metastable zone which shows variations in certain seismicity parameters known as prognostic anomalies. Our results indicate that the variations in seismicity parameters before the two strong earthquakes in the Koyna region have a pattern of prognostic anomalies typical of tectonic earthquakes. We conclude that initiation of failure in a metastable zone can be caused both, by external impacts, reservoir loading and unloading in our case, and internal processes of avalanchelike failure development.
Hydromechanics of the Koyna–Warna Region, India
Pure and Applied Geophysics, 2010
Continuous reservoir-induced seismicity has been observed in the Koyna-Warna region in western India following the beginning of impoundment of Koyna and Warna Reservoirs in 1961 and 1985, respectively. This seismicity includes 19 events with M C 5.0 which occurred in 7 episodes (I-VII) between 1967 and 2005 at non-repeating hypocentral locations. In this study, we examined the first six episodes. The seismicity occurs by diffusion of pore pressures from the reservoirs to hypocentral locations along a saturated, critically stressed network of NE trending faults and NW trending fractures. We used the daily lake levels in the two reservoirs, from impoundment to 2000, to calculate the time history of the diffused pore pressures and their daily rate of change at the hypocentral locations. The results of our analysis indicate that Episodes I and IV are primarily associated with the initial filling of the two reservoirs. The diffused pore pressures are generated by the large (20-45 m) annual fluctuations of lake levels. We interpret that critical excess pore pressures [*300 kPa and [*600 kPa were needed to induce Episodes I-III and Episodes IV-VI, respectively, suggesting the presence of stronger faults in the region. The exceedance of the previous water level maxima (stress memory) was found to be the most important, although not determining factor in inducing the episodes. The annual rise of 40 m or more, rapid filling rates and elevated dp/dt values over a filling cycle, contributed to the rapid increase in pore pressure.
Recent seismicity in Northeast India and its adjoining region
Journal of Seismology, 2008
Recent seismicity in the northeast India and its adjoining region exhibits different earthquake mechanisms - predominantly thrust faulting on the eastern boundary, normal faulting in the upper Himalaya, and strike slip in the remaining areas. A homogenized catalogue in moment magnitude, M W, covering a period from 1906 to 2006 is derived from International Seismological Center (ISC) catalogue, and Global Centroid Moment Tensor (GCMT) database. Owing to significant and stable earthquake recordings as seen from 1964 onwards, the seismicity in the region is analyzed for the period with spatial distribution of magnitude of completeness m t, b value, a value, and correlation fractal dimension D C. The estimated value of m t is found to vary between 4.0 and 4.8. The a value is seen to vary from 4.47 to 8.59 while b value ranges from 0.61 to 1.36. Thrust zones are seen to exhibit predominantly lower b value distribution while strike-slip and normal faulting regimes are associated with moderate to higher b value distribution. D C is found to vary from 0.70 to 1.66. Although the correlation between spatial distribution of b value and D C is seen predominantly negative, positive correlations can also be observed in some parts of this territory. A major observation is the strikingly negative correlation with low b value in the eastern boundary thrust region implying a possible case of extending asperity. Incidentally, application of box counting method on fault segments of the study region indicates comparatively higher fractal dimension, D, suggesting an inclination towards a planar geometrical coverage in the 2D spatial extent. Finally, four broad seismic source zones are demarcated based on the estimated spatial seismicity patterns in collaboration with the underlying active fault networks. The present work appraises the seismicity scenario in fulfillment of a basic groundwork for seismic hazard assessment in this earthquake province of the country.
Journal of Earth System Science, 2015
The northeastern part of Kumaun Lesser Himalaya, Uttarakhand, India, lying between the rupture zones of 1905, Kangra and 1934, Bihar-Nepal earthquakes and known as 'central seismic gap' is a segment of an active fault known to produce significant earthquakes and has not slipped in an unusually long time when compared to other segments. The studied section forms a part of this seismic gap and is seismically an active segment of the Himalayan arc, as compared to the remaining part of the Kumaun Lesser Himalaya and it is evident by active geomorphological features and seismicity data. The geomorphological features of various river valley transects suggest that the region had a history of tectonic rejuvenation which is testified by the deposition of various levels of terraces and their relative uplift, shifting and ponding of river channels, uplifted potholes, triangular facets on fault planes, fault scarps, etc. Further, the seismic data of five-station digital telemetered seismic network along with two stand alone systems show the distribution of earthquakes in or along the analyzed fault transects. It is observed that the microseismic earthquakes (magnitude 1.0-3.0) frequently occur in the region and hypocenters of these earthquakes are confined to shallow depths (10-20 km), with low stress drop values (1.0-10 bar) and higher peak ground velocity (PGV). The cluster of events is observed in the region, sandwiched between the Berinag Thrust (BT) in south and Main Central Thrust (MCT) in north. The occurrences of shallow focus earthquakes and the surface deformational features in the different river valley transect indicates that the region is undergoing neotectonic rejuvenation. In absence of chronology of the deposits it is difficult to relate it with extant seismicity, but from the geomorphic and seismic observations it may be concluded that the region is still tectonically active. The information would be very important in identifying the areas of hazard prone and also planning and designing of the socioeconomic projects.