[S02-P] Poster

[S02-P-01] Spatio-temporal variation in seismicity due to periodically alternating roles of reservoirs in the Koyna-Warna RTS zone, India

^○Amrita Yadav¹, Kalpna Gahalaut², N.Purnachandra Rao² (1.Borehole Geophysics Research Laboratory (NCAOR), Karad, India, 2.CSIR-National Geophysical Research Institute, Hyderabad, India)

Reservoir triggered seismicity (RTS) is well-accepted phenomenon describing the triggering of earthquakes through the local stress change due to the reservoir impoundment. Koyna–Warna region (KWR) in India is one such famous RTS site where earthquakes keep occurring after 50 and 30 years of Koyna(KR) and Warna reservoirs(WR) impoundment respectively and after the large M6.3 Koyna earthquake. Here we analysed the role of the reservoir water levels on spatio-temporal distribution of the earthquakes during 1968–2012. First, we analysed the seismicity data during January 2005-June 2012 recorded by seismic network operated by CSIR-NGRI. We performed a statistical analysis using Singular Spectrum Analysis(SSA) which shows that water level series has dominance of variance for annual periodicity. For the earthquake time series, a zone close to the WR, shows predominance of annual frequency, suggesting a compelling relation between seismicity and reservoir water level changes. To see an overall spatio-temporal effect of the reservoirs on the seismicity of the region, this type of study is required also for the earlier time period. In continuation of the previous work we divided the 1968-2004(MERI catalogue) earthquakes into different zones and performed same analysis. We found the effect of both the long-term and annual variations of the reservoir water level on the seismicity. Also an alternating role of the KR and WR on the seismicity, for the time period 1983-1995 the earthquakes near WR, during 1996-2004 the earthquakes near KR and during 2005-2012 again the earthquakes near WR, was found to be associated with annual variations in reservoir water levels. It appears that during the release of stress in region beneath one reservoir, the region beneath the other reservoir is accumulating stress and once the stress is released from one region other region is activated.