Improved Regional Earthquake Magnitude Scaling Relations for the Indian Subcontinent

This study emphasizes the significance of a homogenous earthquake catalogue for assessing seismicity, seismotectonics, seismic hazard, and seismic risk in a region. While various magnitude scales exist in earthquake catalogs, the homogeneity of these scales, particularly regarding the consistent use of the moment magnitude (Mw) scale for small and intermediate magnitude earthquakes, has been a key point of discussion. According to recent research, lower and intermediate ranges are not encompassed by the Mw scale for worldwide seismicity and ineffectively depict the seismic source potential because of its dependency on surface-wave magnitudes (Ms); thus, a scale called the generalized seismic moment magnitude scale (Mwg), based on direct values of seismic moment (M0), that seamlessly relates seismic source processes should be used. Every study done so far for India has used the homogenized Mw scale earthquake catalogue. To address this concern, this study aims to develop regional earthquake magnitude conversion equations helpful for developing a homogenized earthquake catalog for India in the most recently developed advanced scale, Mwg scale. For this, India is divided into five major regions based on seismotectonics, seismicity, and rupture characteristics. This work presents advanced regional magnitude conversion relations in terms of Mwg scale for each region and the entire country, utilizing data from national, regional, and international seismological agencies. Advanced and standard regression techniques such as standard general orthogonal regression, improved general orthogonal regression, standard least-square regression, and inverted standard least-square regression are employed to establish relationships between Mwg and other magnitude scales (mb, Ms, and ML). This analysis provides valuable insights into the nuances and trade-offs associated with each method. The resulting magnitude conversion relations can be applied to homogenize the earthquake catalogue for the Indian subcontinent, thereby assisting in India’s future seismic hazard assessment.