An ML scale for Eastern Dharwar Craton and adjoining regions

A local magnitude scale has been developed for Eastern Dharwar Craton (EDC) and adjoining areas around Southern Peninsular Shield, India, to improve the scale used previously in this region. Measurements, 1333 of peak amplitudes on simulated Wood-Anderson instruments located in Andhra Pradesh and Telangana (APTS) network for 91 earthquakes recorded at 26 seismic stations have been used to determine a new distance correction curve for routine in calculating the local magnitudes. The new ML scale has been derived using the Grey Wolf Optimization (GWO), a swarm intelligence-based global optimization technique for the first time: $${M}_{\mathrm{L }}=\mathrm{log}A+1.2588\mathrm{log}R +0.0002789R-2.2265$$ , where A is the amplitude measured in millimeters, and R is the hypocentral distance in kilometers. The new ML scale derived here is valid up to 400 km. This study has been carried out using both singular value decomposition (SVD) and GWO to obtain scale coefficients and station corrections. The newly derived scale has a drop of 21.37% in the overall standard deviation of all magnitude residuals when station corrections are considered in comparison to the previously used scale. A new ML-MW relationship was derived for local magnitudes above 2.5, and the relationship was MW α 0.9224*ML. In our study, the results obtained using GWO gave less standard deviation of all magnitude residuals for the Eastern Dharwar Craton, thus proving to be better than the conventional SVD approach.