Abstract
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.
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Acknowledgements
I would like to thank the Director, CSIR-NGRI, for his permission to allow me for summer training in this institute. I took inspiration from Ottemöller and Sargeant (2013), while preparing figures.
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Aman Sharma: conceptualization, methodology, software; Divakar Vashisth: methodology, software; Naresh Bandari: data curation, software; G Suresh: data curation, investigation; P Solomon Raju: conceptualization, methodology, original draft preparation; R Vijaya Raghavan: software, D Srinagesh: supervision, validation, reviewing and editing.
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Highlights
In this study, we calibrated a new ML scale for EDC and adjoining regions (Southern Peninsular Shield, India), which could replace the earlier used ML scale for computing local magnitudes in this region.
We processed waveforms from about 91 earthquakes to extract synthetic Wood-Anderson displacements over which the measurements of peak amplitude were performed. Following the original definition of Richter, we used both the horizontal components of the simulated Wood-Anderson seismogram for amplitude picks.
We performed SVD and GWO inversion on our dataset and derived the values of scale coefficients and correction coefficients and calculated the magnitude residual for assessment of the new relationship.
This scale has a drop of 21.37% in the overall standard deviation of all magnitude residuals when station corrections are considered.
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Sharma, A., Vashisth, D., Naresh, B. et al. An ML scale for Eastern Dharwar Craton and adjoining regions. J Seismol 25, 1251–1263 (2021). https://doi.org/10.1007/s10950-021-10028-x
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DOI: https://doi.org/10.1007/s10950-021-10028-x