The Sub-Himalayan fold-thrust belt in the 1905-Kangra earthquake zone: A critical taper model perspective for Seismic Hazard Assessment

摘要

We investigate the broader epicentral area of the M=7.8, 1905 Kangra earthquake(s), North India, affecting the Sub-Himalayan hills. The tectonics of the area is characterised by two major rentrants (Kangra and Dehradun) interposed by the Nahan Salient. The first order topography between the Himalayan Frontal Thrust and the Main Boundary Thrust shows a marked lateral variation along strike of the mean gradient, characterised by a very small mean slope angle (ca. 1°) in correspondence with the reentrants and higher values (ca. 3°) in the salient. These tectonic and topographic features also show a good correspondence with the peculiar macroseismic field of the 1905 event(s), which is characterised by two distinct intensity maxima, separated by a distance of about 150 km, clearly overlapping the two major tectonic reentrants. In this paper, based on available geological and geophysical information and a critical analysis of the general mechanical constraints, the seismogenic volume of the external sector of the chain is investigated in terms of critical taper model attempting to clarify the possible correlations between tectonics, topography and seismicity in the Sub-Himalayan belt. Based on different assumptions three possible seismotectonic scenarios are explored in order to constrain their likelihood and therefore suggest a potential seismic gap in the area corresponding to the Nahan Salient, which may experience in the future an event of significant magnitude.