Spatio-temporal mapping of seismicity parameters in Shillong Plateau and adjoining regions

The Shillong Plateau (SP) is globally renowned for its high seismic activity. The seismicity is mainly caused by the subduction of the Indian plate beneath the Eurasian and Burmese plates in the north and west respectively, in addition to the popup of SP. In the present study, we analyse the seismicity of the SP and adjoining region bounded by latitude from 22.8°N to 28.5°N and longitude 87.5°E to 95.5°E using earthquake data of 825-2024 acquired from national, international, and literature sources. Ten time windows namely 825-2024, 2019-2024, 2008-2018, 825-1800, 1997-2007, 1986-1996, 1975-1985, 1964-1974, 1901-1963, and 1801-1900 have been considered to estimate and compare the spatio-temporal variation of seismicity parameters. We estimated the spatio-temporal variation of the magnitude of completeness (M_C), a-value, b-value, and fractal dimension (D_C) of the considered region. M_C, a-value, and b-value for the above time windows range from 4.70 to 5.70, 4.36 to 9.85, 0.52 to 1.59, however, spatial mapping of M_C, a-value, and b-value at each node of the grid of 0.05°×0.05° range from 4.10 to 5.82, 4.46 to 18.94, 0.58 to 3.66 respectively. Spatial mapping of D_C at each node of the grid of 1°×1° and 0.5°×0.5° range from 0.258 to 2.240 and 0.462 to 2.164 respectively, however, temporal variation of D_C ranges from 0.344 to 2.842. The relationship between b-values for 825-2024 and D_C-values shows a positive correlation, while a negative correlation exists between -values and D_C-values. The spatio-temporal distributions of these parameters reveal insights into the regional variation of stress levels and geological complexity, which can be used as input for seismic hazard estimation.