Periodic variation of stress field in the Koyna–Warna reservoir triggered seismic zone inferred from focal mechanism studies

Rao, N. Purnachandra; Shashidhar, D.

doi:10.1016/j.tecto.2016.04.036

Cited by 40 publications

(16 citation statements)

References 47 publications

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“…The Koyna‐warna reservoir in India is one of the mostly studied RTS sites in the world. As another typical example of protracted seismicity, it shares many similarities with the XWR, such as the dam height, seismicity activity after impoundment, and the focal mechanisms of earthquakes (Bhattacharya, ; Rao & Shashidhar, ; Shashidhar et al, ). For example, both reservoirs have triggered M6 earthquakes within several years after impoundment, and numerous earthquakes continue to happen till today, including tens of M4 ones.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, earthquake depth in XWR migrates gradually to deeper depth and currently concentrates at 5–10‐km depth. On the contrary, earthquakes in Koyna‐warna reservoir still spread from near surface to more than 10 km from south to north (Dixit et al, ; Gupta, ; Rao & Shashidhar, ). Third, the distribution of earthquake type of XWR has dichotomy pattern in and outside reservoir area, but Koyna‐warna reservoir earthquakes do not have such a pattern.…”

Section: Discussionmentioning

confidence: 99%

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Upper Crustal Structure and Earthquake Mechanism in the Xinfengjiang Water Reservoir, Guangdong, China

Sun

Yang

et al. 2018

JGR Solid Earth

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The Xinfengjiang Water Reservoir (XWR) in Guangdong, China, is one of the reservoirs that have triggered earthquakes of magnitudes greater than 6. Numerous earthquakes have occurred since the impoundment of the reservoir, making it one of the most active seismic zones in Guangdong. However, due to the lack of seismic stations, the detailed seismic structures and earthquake mechanisms within XWR have not been resolved, and the significance of XWR as a typical protracted earthquake location is not well judged. In this study, by collecting waveform data from both permanent and temporary stations from 2012 to 2015, we relocated 1,528 earthquakes and inverted both V p and V s structures from traveltimes of these earthquakes. Using waveform data, we also investigated focal mechanisms of earthquakes with magnitude greater than 1.5 in this region. Our results reveal fine crustal structure that has never been shown before and show complicated crust structure with several low-velocity zones extending to 5-10 km depth under the major faults. Earthquake focal mechanisms show more dip-slip faults than strike-slip faults, and the two types of earthquakes are roughly divided by the reservoir boundary. The direction of principle stress of the earthquakes is northwest-southeast, consistent with the direction of tectonic principal stress. Combining the above results, and investigation of historical earthquakes and water level change, we suggest that water loading cycle and diffusion play important role in XWR seismicity. They increase the pore pressure, make the earthquakes migrate to deeper depth, and change the type of earthquakes.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Upper Crustal Structure and Earthquake Mechanism in the Xinfengjiang Water Reservoir, Guangdong, China

Sun

Yang

et al. 2018

JGR Solid Earth

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“…The uncertainty in the estimates is likely attributable to the geological heterogeneity of the basement granitoids in terms of varying grain size, varying degrees of shearing, and varying fracture density along depth that cause substantial heterogeneity in mechanical properties (Goswami, Akkiraju, Misra , et al, ,Goswami, Akkiraju, Singh, et al, ). Nevertheless, the estimates confirm the general NNE to NNW orientations constrained from inversion of well‐determined focal mechanisms of 50 earthquakes of M ≥ 3.6 in the Koyna and Warna regions (Rao & Shashidhar, ) and suggest that the S Hmax orientation obtained from borehole KFD1 data sets is representative of the region. The mean orientations of S Hmax obtained individually from borehole breakouts, A‐DITFs and earthquake focal mechanisms are listed in Table .…”

Section: Discussionmentioning

confidence: 82%

In Situ Stress Orientation From 3 km Borehole Image Logs in the Koyna Seismogenic Zone, Western India: Implications for Transitional Faulting Environment

2020

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Knowledge of the in situ stress regime is critical to investigate the genesis of recurrent triggered seismicity over the past five decades in the Koyna seismogenic zone. Orientations of in situ horizontal stresses are determined for the first time from analyses of image logs in a 3 km deep scientific borehole KFD1 in the area. KFD1 passed through 1,247 m thick Deccan Traps and continued 1,767 m in the granitic basement. Stress-induced wellbore failures, breakouts and drilling-induced tensile fractures, are identified in the acoustic and microresistivity images of the granitic basement. Additionally, tightly constrained focal mechanisms of 50 earthquakes of M ≥ 3.6, reported in literature, are inverted to constrain the stress regime. Salient results are as follows: (i) wellbore breakouts and drilling-induced tensile fractures constrain N9°W ± 17°orientation for maximum horizontal principal stress (S Hmax ); (ii) consistency with the regional NNW-SSE orientation of S Hmax from inversion of earthquake focal mechanisms shows that the borehole data are representative for the Koyna region; (iii) breakout rotations at multiple depths below 2,100 m indicate that the borehole may have passed through localized fault damage zones; (iv) consistent strike azimuths of steeply dipping fractures with S Hmax orientation indicate favorable conditions for strike-slip to normal transitional faulting environment; and (v) stress inversion of 50 well-determined earthquake focal mechanisms supports transitional faulting environment in the Koyna seismogenic zone. Thus, stress orientation and fracture information from borehole data, together with stress regime constrained from inversion of earthquake focal mechanisms, shed new light on the faulting environment in the region.

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“…In the early stage, earthquakes confined to a smaller region of 20 km 2 around the Koyna Dam, but the seismicity extended further south due to the filling of the Warna reservoir in 1985 (Rastogi et al, ). Earthquakes in the region are mostly shallower than 10 km (Gupta, ; Rao & Shashidhar, ), occurring mainly in low‐velocity zones at depths of 0–1 and 5–10 km (Mandal et al, ).…”

Section: Study Regionmentioning

confidence: 99%

“…Several studies were carried out in the past to understand seismicity, stress field, and tectonics of the region. Rao and Shashidhar () found a periodic variation of the stress field in the Koyna‐Warna region accompanied by accumulation and release of stress due to the horizontal convergence of the Indian plate. However, the stress changes due to reservoir load are very small, on the order of 0.1 MPa as compared to typical stress drops on the order of 10–20 MPa in this region (Mandal et al, ).…”

Section: Study Regionmentioning

confidence: 99%

Remote Triggering in the Koyna‐Warna Reservoir‐Induced Seismic Zone, Western India

et al. 2018

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Dynamic triggering following large distant earthquakes has been observed in many regions globally. In this study, we present evidence for remote dynamic triggering in the Koyna‐Warna region of Western India, which is known to be a premier site of reservoir‐induced seismicity. Using data from a closely spaced broadband network of 11 stations operated in the region since 2005, we conduct a systematic search for dynamic triggering following 20 large distant earthquakes with dynamic stresses of at least 1 kPa in the region. We find that the only positive cases of dynamic triggering occurred during 11 April 2012, Mw8.6 Indian Ocean earthquake and its largest aftershock of Mw8.2. In the first case, microearthquakes started to occur in the first few cycles of the Love waves, and the largest event of magnitude 3.3 occurred during the first few cycles of the Rayleigh waves. The increase of microseismicity lasted for up to five days, including a magnitude 4.8 event occurred approximately three days later. Our results suggest that the Koyna‐Warna region is stress sensitive and susceptible for remote dynamic triggering, although the apparent triggering threshold appears to be slightly higher than other regions.

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Periodic variation of stress field in the Koyna–Warna reservoir triggered seismic zone inferred from focal mechanism studies

Cited by 40 publications

References 47 publications

Upper Crustal Structure and Earthquake Mechanism in the Xinfengjiang Water Reservoir, Guangdong, China

Upper Crustal Structure and Earthquake Mechanism in the Xinfengjiang Water Reservoir, Guangdong, China

In Situ Stress Orientation From 3 km Borehole Image Logs in the Koyna Seismogenic Zone, Western India: Implications for Transitional Faulting Environment

Remote Triggering in the Koyna‐Warna Reservoir‐Induced Seismic Zone, Western India

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