Characterization of earthquake hazard at the Palghar and Pulichintala swarm activity regions (India) through three-dimensional modelling of b-value and fractal (correlation) dimensions

The present work focuses on the three-dimensional mapping of fractal correlation dimensions and b-values of the Palghar (Maharashtra) and Pulichintala (Andhra Pradesh) regions of the Indian shield. The study is done using catalogues of 8766 Palghar earthquakes of ML0.4–4.7 and 965 Puclichintala earthquakes of ML ranging from −0.4 to 4.6. The b-values are estimated using the maximum likelihood approach, while fractal dimensions are modelled using the correlation dimension approach. The b-value is modelled to be 0.88 ± 0.02 for the Palghar sequence and 0.75 ± 0.04 for the Pulichintala sequence. The modelled b- and D2-values vary from 0.1 to 2.5 and 0.39 to 2.62, respectively, for the Palghar sequence, while they vary from 0.2 to 1.68, and 0.68 to 3.0, respectively, for the Pulichintala sequence. The modelled large b-value (~ 2.5) for the Palghar sequence in particular signifies the typical characteristic of swarm earthquakes. We examine the b-D2 correlations for both the swarm activity sequences and found a positive correlation (i.e. D2 = 1.085 + 0.0015b) for the Palghar sequence while a negative correlation (i.e. D2 = 0.99–0.0414b) for the Pulichintala sequence. The spatial distribution of D2 and b-values suggests that the seismicity in the Palghar region is occurring in the areas with lower to moderate b-values and moderate correlation dimensions, while the seismicity in the Pulichintala region is occurring in areas with moderate b-values and higher D2 values. Based on our results, we interpret the Palghar region as a high tectonic stress region, which can generate moderate earthquakes in future, while the Pulichintala region is a low stress region that can accumulate low levels of tectonic stress posing relatively less earthquake hazard.