Temporal Dynamics of Reservoir-Triggered Seismicity in the Koyna-Warna Region, India: Insights from Fractal Dimension and b-Values

ABSTRACT

We analyse the temporal variation of Reservoir Triggered Seismicity (RTS) in the Koyna-Warna region, India, between 2006 and 2017 using fractal dimension and b-values. The study employs the Allan Fractal Method (AFM) and the Maximum Likelihood Method (MLM) to calculate fractal exponents and b-values. The Dynamic Allan Deviation (DAD) shows consistent behaviour across varying sliding windows (30, 60, and 180), indicating non-random temporal seismicity. The estimated average fractal dimension of 0.041 suggests low-dimensional, non-random dynamics may be associated with systematic annual variation in seismicity observed in this region. It is noticed that the Fractal Dimension (FD) spikes during seismic clusters and drops during quiet periods. The b-values exhibited an inverse relationship with fractal dimensions, with a precursory drop before ML ≥ 4 earthquakes. Gradual decreases in fractal dimensions precede major earthquakes, followed by sharp increases due to aftershocks. This aligns with Mogi’s Type II sequence model. Our results suggest that, (i) Fractal dimension and b-values are sensitive to foreshocks and aftershocks and hence prediction of mainshock is not reliable when the sequence doesn’t match with Mogi’s type II model, (ii) RTS of the Koyna Warna region shows low-dimensional, non-random dynamics characterised by stochastic or chaotic process, and (iii) very low average fractal dimension noticed in Koyna Warna region indicate the systematic cyclic variations of stress due to cyclic changes in the loading/pore pressure. These results provide insights into the linkage of b-value and fractal dimension with the stress and crustal rock heterogeneity of RTS at the Koyna Warna region and support global seismic clustering models, particularly in reservoir-induced contexts.