Delineation of Active Faults, Nucleation Process and Pore Pressure Measurements at Koyna (India)

Abstract

Earthquakes continue to occur in the vicinity of Shivaji Sagar Lake since its creation by the Koyna Dam in 1962. The seismicity peaked in 1967 with a M 6.3 earthquake which claimed over 200 human lives and destroyed the Koyna township. Earthquakes of M`4 occur every year following an increase of water level in the reservoir. During 1973During , 1980During and 1993 earthquakes exceeding magnitude 5 occurred. Most earthquakes of M`4 are associated with pronounced foreshocks and aftershocks. Starting Sepember 1993, seismic monitoring was vastly improved with the deployment of additional close-by stations (analog and digital). The focal parameters now available have enabled delineation of the active faults and deciphering of the earthquake nucleation process. During 1995 -96, 13 boreholes were drilled to depths of 130 to 250 m and measurement of water levels in these wells was initiated. A preliminary analysis of one year's data from a borehole 1 km south of Koyna reveals tidal signatures, indicating connection of the well to a confined aquifer which is favorable for detection of pore pressure anomalies induced by crustal strain. We hope to improve our understanding of the genesis of reservoir-induced earthquakes at Koyna with these new measurements.

Microearthquake Seismology and Seismotectonics of South Asia

“…7.39b). A similar observation of two seismicity trends was also made by Chadha et al (1997), who relocated the lower magnitude (M<3.0) earthquakes in the region (Fig. 7.40a).…”

“…7.40a). , -December, 1994, relocated by Chadha et al (1997); seismic stations are shown by small rectangles, (b) microseismicity, April 1996-December 1997, located by a 10-station digital network (Rai et al, 1999b), and (c) the seismicity with fault plane solutions ).…”

Structure of the Koyna‐Warna Seismic Zone, Maharashtra, India: A possible model for large induced earthquakes elsewhere

“…Several researchers have divided the seismic events into discrete clusters based on location, alignments, and focal mechanisms. The westernmost ~NNE tending cluster of events between Koyna and Warna reservoirs has been referred to as the Koyna River Fault Zone (KRFZ) [ Talwani , ; Pandey and Chadha , ; Bhattacharya , ; Dura‐Gomez and Talwani , ; Shashidhar et al , ; Figure 2a], Cluster 1 [ Chadha et al , ; Figure 2a], the Koyna Seismic Zone (KSZ) [ Gahalaut et al , ; Figure 2b], the Northern Escarpment Zone (NEZ) [ Rai et al , ; Srinagesh and Sarma , ; Sarma and Srinagesh , ; Figure 2b], or the North and South Koyna Clusters [ Mandal et al , ; Figure 2c]. Chadha et al [] identified a second (eastern) ~NNE trending cluster of events between Koyna and Warna reservoirs, which they refer to as Cluster 2 (Figure a).…”

“…The westernmost ~NNE tending cluster of events between Koyna and Warna reservoirs has been referred to as the Koyna River Fault Zone (KRFZ) [ Talwani , ; Pandey and Chadha , ; Bhattacharya , ; Dura‐Gomez and Talwani , ; Shashidhar et al , ; Figure 2a], Cluster 1 [ Chadha et al , ; Figure 2a], the Koyna Seismic Zone (KSZ) [ Gahalaut et al , ; Figure 2b], the Northern Escarpment Zone (NEZ) [ Rai et al , ; Srinagesh and Sarma , ; Sarma and Srinagesh , ; Figure 2b], or the North and South Koyna Clusters [ Mandal et al , ; Figure 2c]. Chadha et al [] identified a second (eastern) ~NNE trending cluster of events between Koyna and Warna reservoirs, which they refer to as Cluster 2 (Figure a). The earthquake clusters have also been divided into two SE trending clusters of events, the southernmost of which is referred to as the Southern Escarpment Zone (SEZ) [ Rai et al , ; Srinagesh and Sarma , ; Sarma and Srinagesh , ; Figure 2b] and the more northeasterly cluster near Warna Reservoir is referred to as the Warna Seismic Zone (WSZ) [ Rai et al , ; Srinagesh and Sarma , ; Sarma and Srinagesh , ] (Figure b).…”

“…The Koyna‐Warna region is one of the most studied sites for RIS [ Gupta et al , , ; Guha et al , ; Simpson , ; Rastogi and Talwani , ; Langston and Franco‐Spera , ; Chadha et al , ; Talwani , ; Mandal et al , ; Rai et al , ; Rajendran and Harish , ; Gahalaut et al , ; Srinagesh and Sarma , ; Dura‐Gomez and Talwani , ; Bhattacharya , ; Shashidhar et al , ; Dixit et al , ]. The temporal correlation of larger magnitude earthquakes following large reservoir‐filling monsoons has been recognized for some time [ Talwani , ; Gupta , ; Dura‐Gomez and Talwani , ], and the temporal‐spatial correlation of larger (M>5) earthquakes in the Koyna area has also been thoroughly investigated [ Talwani , ; Dura‐Gomez and Talwani , ].…”