A study of Guptkashi, Uttarakhand earthquake of 6 February 2017 (<italic>M</italic><italic>w</italic>5.3) in the Himalayan arc and implications for ground motion estimation.

The 2017 Guptkashi earthquake occurred in a segment of the Himalayan arc with high potential for a strong earthquake in the near future. In this context, a careful analysis of the earthquake is important as it may shed light on source and ground motion characteristics during future earthquakes. Using the earthquake recording on a single broadband strong-motion seismograph installed at the epicenter, we estimate the earthquake’s location (30.546° N, 79.063° E), depth (<italic>H</italic> = 19 km), the seismic moment (<italic>M</italic>0 = 1.12×1017 Nm, <italic>M</italic><italic>w</italic>5.3), the focal mechanism (<italic>φ</italic> = 280°, <italic>δ</italic> = 14°, <italic>λ</italic> = 84°), the source radius (<italic>a</italic> = 1.3 km), and the static stress drop (Δ<italic>σ</italic><italic>s</italic>~22 MPa). The event occurred just above the Main Himalayan Thrust. S-wave spectra of the earthquake at hard sites in the arc are well approximated (assuming <italic>ω</italic>−2 source model) by attenuation parameters <italic>Q</italic>(<italic>f</italic>) = 500<italic>f</italic>0.9, <italic>κ</italic> = 0.04 s, and <italic>f</italic>max = infinite, and a stress drop of Δ<italic>σ</italic> = 70 MPa. Observed and computed peak ground motions, using stochastic method along with parameters inferred from spectral analysis, agree well with each other. These attenuation parameters are also reasonable for the observed spectra and/or peak ground motion parameters in the arc at distances ≤ 200 km during five other earthquakes in the region (4.6 ≤ <italic>M</italic><italic>w</italic> ≤ 6.9). The estimated stress drop of the six events ranges from 20 to 120 MPa. Our analysis suggests that attenuation parameters given above may be used for ground motion estimation at hard sites in the Himalayan arc via the stochastic method. [ABSTRACT FROM AUTHOR]