Geotechnical Susceptibility Constraints on Seismicity of Karewa Group and Its Implication in Quaternary Earthquakes Around Kashmir Valley, India

摘要

The seismically sensitive soft sediment deformations of Karewa Group have been geotechni-cally analysed to explore the status and frequency of past Quaternary earthquakes in Kashmir valley, India. The detailed studies were performed to establish the sequences of sedimentary structures in general and deformed structures in particular in view of geotechnical parameters. For the purpose the collected sediments from different deformed zones were analysed as per American Standard of Testing Materials for determination of size gradations, liquid limit, plastic limit and flow indices. The studied sequences of deformations were established in space and time by using empirically relationship. The structural architectures of sedimentary features (cross-beddings, massive beddings/loads) reveal the fluvial environments of fluctuating energy conditions for formation of sediment successions. In addition, the sandwiched-zonations of some peculiar structures preserved in the litho-succession may be formed through mechanism different from sedimentations. The size distribution of sediments from sandwiched-zone exhibits medium to fine sands and silt with sorting coefficients ranging from 1.21 to 2.54, coefficient of uniformity ranging from 1.26 to 3.6 with some exceptional values like 5.0, 16.6 and coefficient of curvature ranging from 0.67 to 1.80. The sediments of the same zone show the values of liquidity index ranging from 0.16 to 0.88 and plasticity index ranging from 3.69 to 18.57 with low blows values. These above size sensitive geotechnical parameter values show the higher flow indices and least resistance to flow. The sediments of the peculiar structural zone with characteristically higher flow indices and low resistance support the formation of the soft-sediment structures under seismic stress condition. The demarcated sandwiched zones with such conditions at the time frame of 1,06,566.6 years, 93,245.8 years and 54,502.8 years ago from recent appears to supports three prominent earthquake events (I, II and III) in the geological history of Quaternary deposits around Kashmir Valley, India.