Three-dimensional b-value and Fractal Dimension Mapping of the Uttarakhand Himalayan Region

Abstract

Abstract The 3-D distributions of b-value of the frequency-magnitude distribution and fractal correlation dimension (D2) of seismically active Uttarakhand Himalayan seismic zone is presented. For this study, a catalogue of 525 local earthquakes was used (ML1.0-5.5) during 2017-2020. The de-clustered catalog is found to be complete above ML=2.6. The b-value is estimated to be 0.82±0.06 by maximum likelihood method. The modelled b- and D2 estimates in the study area range from 0.35 to 1.524 and 0.29 to 1.71, respectively. The present study reveals a negative b-D2 relationship (i.e. D2=-0.008b + 1.536, with a correlation coefficient of 0.9892) with week clustering. The modeling detects two zones (viz., A, and B) of high D2 and low b-values within the MCT zone, which are defined as high hazard zones (HHZ) while zone C (in the SE part of the MCT zone) with high D2 and high b-values is detected as an intermediate hazard zone. Also, three zones (D, E and F) with low D2 and low b-values are identified as low hazard zones (LHZ), which are located away from the MCT zone. The A and B high hazard zones can accumulate high levels of tectonic stress and pose risks for generating large earthquakes in the future. But, IHZ-C represents intermediate hazard level that can generate M≥5 events in future. The mapped A and B zones are inferred to be most hazardous in the region, which correlate well with recognized seismogeneic nodes capable of M6.5+ earthquakes in the region as suggested by the geomorphological zoning using pattern recognition.