Distribution of active tectonics in the Himalayan piedmont (Darjeeling, Eastern India) inferred from Horizontal-to-Vertical Spectral Ratio analysis of passive seismic records
Résumé
Active tectonics necessitate to select key zones for detailed studies. In the Himalaya, and specially in its piedmont, the quality of natural outcrops is poor due to strong weathering, heavy vegetation and/or anthropogenic influence. In this paper, we show that the HVSR (Horizontal-to-Vertical Spectral Ratio) method allows exploring the structures beneath the 2-Active tectonics in the Darjeeling piedmont Terra Nova plain south of the Himalayan mountain front. This method is easy to apply in any context and we show that it has allowed revealing the subsurface structures down to 600 meters even in jungle areas. We have correlated geomorphologic scarps evidenced by geomorphologic profiles but nearly invisible in the jungle, to thrust structures evidenced at depth. Two of these scarps of about ten meters affect the 3.7 ± 0.7 ka old surface and imply that about half of the convergence is expressed south of the Himalayan front in this zone.
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