Moment tensor inversion and uncertainty analysis of earthquakes in Garhwal-Kumaon Himalayas

Summary This study presents the moment tensor catalog of 40 small-to-moderate earthquakes (MW ≥3.5) in the Garhwal-Kumaon region of the northwestern Himalayas. We use the cut-and-paste approach to estimate the moment tensor and to quantify uncertainty in solutions. Observed data from local and regional broadband networks are used to see the impact of station distribution on moment tensor solutions. A 1-dimensional local velocity model is used to compute Green’s functions for generating the synthetic waveforms. The analysis reveals that combining local and regional networks significantly reduces the moment tensor uncertainties, with the local data set generally yielding a more stable solution than the regional one. Additionally, incorporating the first-motion polarity information along with waveform data provides robust solutions. Our moment tensor catalog has 21 earthquakes with thrust mechanisms, 4 with normal mechanisms, and 15 with oblique mechanisms. The systematically observed negative time shifts across most stations suggest that the actual velocity model is faster than the one assumed. This is most likely due to the unaccounted heterogeneous structure and inaccuracy in the 1D velocity model. The findings of this study will be beneficial in the advancement of 3D seismic imaging of the Himalayas and offer significant insights into the seismotectonics of the Garhwal-Kumaon Himalayas.