Seismicity of Jharkhand state resembles to that of Stable Continental Region (SCR) and has experienced nearly 30 earthquakes of magnitudes ranging from 3 to 6 during the last 147 years. These earthquakes are shallow and crustal in nature which are scattered all over the region. However during the last 10 to 15 years there has been increase in the occurrence of seismic events. The study of plot of earthquake energy release versus time indicates that the earthquake of magnitude 6 may occur in and around the year 2060. The probabilistic analysis shows a high probability of occurrence of seismic events with M > 5 in 50 years of time interval and such interval increases with increase of earthquake magnitude. The return period for magnitudes 6 and above is quite high (80 to 100 years) where as for lower magnitudes the probability of occurrence ranges from 7 to 22 years. This periodicity of 100 years for magnitude 6 is approximately matching with the trend of magnitude energy release plot. However in view of the development and upcoming of high rise buildings in the region the smaller events and longer return period of damaging earthquake must not be ignored.

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In this paper, we demonstrate the potential of the elastic full waveform inversion to overcome some difficult challenges in onshore seismic imaging. The approach allows for simultaneous inversion of surface and body waves and, theoretically, is free from the limitations of traditional dispersion curve analysis and traveltime inversion. Indeed, identification and separation of different wavefield types are not required and all wave types can be treated within a unified inversion scheme. However, full waveform inversion requires a reasonably good initial model and the sensitivity of the misfit function with respect to the different wave types should be appropriately accounted for. This is the most essential step with onshore seismic data, since the ground roll is much more energetic in comparison with the body waves. Our approach is based on a time-offset weighting function to balance the contribution of the different wave types in combination with a conventional frequency continuation approach. We first illustrate the feasibility of the proposed approach on a 2D synthetic example representing a complex geology from south Oman. Then we present a 3D real data example from south Oman, where application of our workflow till 8 Hz plays a pivotal role in retrieving a reliable model and in explaining the entire observed wavefields. In this example, the inversion of the ground-roll helps improving the recovery of the shallow part of the Earth, and hence better constraining the inversion of the body waves.

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