• M Ravi Kumar

      Articles written in Journal of Earth System Science

    • Comparison of earthquake source characteristics in the Kachchh Rift Basin and Saurashtra horst, Deccan Volcanic Province, western India

      B Sairam A P Singh M Ravi Kumar

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      Seismic source parameters of small to moderate sized intraplate earthquakes that occurred during 2002–2009 in the tectonic blocks of Kachchh Rift Basin (KRB) and the Saurashtra Horst (SH), in the stable continental region of western peninsular India, are studied through spectral analysis of shear waves. The data of aftershock sequence of the 2001 Bhuj earthquake (Mw 7.7) in the KRB and the 2007 Talala earthquake (Mw 5.0) in the SH are used for this study. In the SH, the seismic moment (Mo), corner frequency (fc), stress drop (Δ σ) and source radius (r) vary from 7.8 × 10 ¹¹ to 4.0×10 ¹⁶ N-m, 1.0–8.9 Hz, 4.8–10.2 MPa and 195–1480 m, respectively. While in the KRB, these parameters vary from Mo ∼ 1.24 × 10 ¹¹ to 4.1×10 ¹⁶ N-m, fc ~ 1.6 to 13.1 Hz, Δ σ ~ 0.06 to 16.62 MPa and r ~ 100 to 840 m. The kappa (K) value in the KRB (0.025–0.03) is slightly larger than that in the SH region (0.02), probably due to thick sedimentary layers. The estimated stress drops of earthquakes in the KRB are relativelyhigher than those in SH, due to large crustal stress concentration associated with mafic/ultramafic rocks at the hypocentral depths. The results also suggest that the stress drop value of intraplate earthquakes is larger than the interplate earthquakes. In addition, it is observed that the strike-slip events in the SH have lower stress drops, compared to the thrust and strike-slip events.

    • Microseism source distribution inferred from noise recordings at the Gujarat Seismic Network, India


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      We analyse continuous seismic ambient noise data recorded by the Gujarat Seismic Network during 2015 to characterise ambient noise sources and their directionality. We use probabilistic power spectral densities and single-station three-component polarisation techniques to estimate the noise levels at individual stations and noise source azimuthal distribution. The spectral power at short- and long-period ambient noise in the coastal regions of the southern part of Gujarat matches well with the global high-noise models, whereas the noise level in the northern part is in conformity with the global mean. Quarterly variation of power in the primary (PM) and secondary microseism (SM) bands suggests high-noise levels during the monsoon season. We observed high and moderate PM and SM noise powers at stations near the faults in the Kachchh region and the coastal areas of southern Gujarat, respectively. The azimuths of strong PM and SM sources estimated from the single-station polarisation method indicate that the main sources of noise are in the Indian Ocean and the Arabian Sea. We also observed a seasonal variation in the polarised signal azimuth and power. In addition to the noise source distribution, analysis of spatially averaged ambient noise levels in the PM and SM bands suggests a possible association of ambient noise levels with subsurface characteristics and regional faults in the study area.

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