Complexity in hydro-seismicity of the Koyna-Warna region, India

Koyna-Warna region in western India is known to be the largest case of the reservoir-triggered seismicity in the world with M6.3 earthquake in 1967. This region continues to be seismically active even after 45 years with occurrences of earthquakes up to M5.0. The porous crustal rocks of Koyna-Warna region respond to changes in the prevailing stress/strain regime. This crustal section is highly fractured and is being fed by rivers and reservoirs. It is also subjected to fluctuating plate boundary forces and significant gravity-induced stresses due to crustal inhomogeneities. These changes induce variations in the water level in bore wells before, during and after an earthquake, and their study can help in understanding the earthquake genesis in the region. The ongoing seismicity thus requires understanding of coupled hydrological and tectonic processes in the region. Water table fluctuations are a reflection of the ongoing hydro-tectonics of the region. The fractal dimension of water levels in the bore wells of the region can be used as measure of the nonlinear characteristics of porous rock, revealing the underlying complexity. In this paper, we present values of correlation dimensions of the water level data in the bore wells using the nonlinear time series methodology. The spatiotemporal changes in the fractal dimensions have also been determined. The results show that hydro-seismically the region behaves as a low-dimensional nonlinear dynamical system.