Abstract
Many studies based on the geodetic data and statistical analysis of seismicity have pointed out that sufficient amount of stress accumulated in the Himalayan plate boundary may host a big earthquake. Consequently, high seismic activities and infrastructural developments in the major cities around Himalayan regions are always of major concern. The ground motion parameter estimation plays a vital role in the near real time evaluation of potentially damaged areas and helps in mitigating the seismic hazard. Therefore, keeping in mind the importance of estimation of ground motion parameters, we targeted two moderate-size earthquakes that occurred recently within a gap of 10 months in Uttarakhand region with M > 5.0 on 06/02/2017 and 06/12/2017. The ground motions are simulated by adopting a stochastic modeling technique. The source is assumed as ω−2, a circular point source (Brune’s model). The average value of reported anelastic attenuation from various studies, the quality factor, Qs= 130.4*(f0.996), and stress drop values obtained through iterative procedure are considered for simulations. The stochastic spectra are generated between 0.1 and 10 Hz of frequency range. The site effect is also estimated by using the H/V method in the same frequency range. The synthetic spectra are compared with the observed Fourier amplitude spectra obtained from the recorded waveform data and converted back to the time histories. The stochastic time histories are compared with the observed waveforms and discussed in terms of amplitude (PGA). The simulated and observed response spectra at different structural periods are also discussed. The mismatch between the observed and simulated PGA values along with the GMPE existing for shallow crustal earthquakes is also discussed in the present work.
Highlights
The much evident Himalayan seismicity is attributed to the collision between the Indian and Eurasian plate
The stochastic simulation of two earthquakes, Guptakashi and Ukhimath with magnitudes mb 5.6 and mb 5.1, which occurred at shallow depths of 16.1 and 10 km, respectively, has been attempted
The simulation is done for two earthquakes that occurred in Uttarkashi with magnitude M > 5 on 06/02/2017 and 06/12/2017 [Guptakashi and Ukhimath, respectively]
Summary
The much evident Himalayan seismicity is attributed to the collision between the Indian and Eurasian plate. In this study, the modeled acceleration spectra is structured by using source and medium information at first, and it is corrected by the local site effects beneath each recording station, which is estimated empirically using the H/V method (Nakamura, 1989; 2008). The work of Joshi, 2006a, 2006b; Chopra et al, 2012; Sharma et al, 2014; Kumar et al, 2014 suggest the similar values for the stress drop for the western Himalayan region These values are further used to calculate the corner frequency fc and the source radius r0 of both the Guptakashi and Ukhimath earthquakes for the analysis (please refer to Table 1 for the values).
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