Remnants of large magnitude earthquakes: Evidences from the Great Rann sediments, Kachchh, Western India

During our investigations on the seismicity of the Kachchh region of Gujarat, we recorded a variety of seismically-induced deformational features from the Great Rann sediments. The structures identified, viz. small-scale folding, pseudo-sand blow, sand dike and micro-faulting from the newly-excavated trenches are attributed to liquefaction and fluidization of water-saturated sediment resulting due to upward propagation of cyclic shear waves, generated during earthquake. Other features identified were craters with no connecting feeder dikes from the bottom. We envisage that these craters might have been formed due to sudden down slip along en-echelon faults developed at the crest and on the limb of an anticlinal structure (? Ludiya anticline), suggestive of reactivation of anticlinal structure caused by the tectonic movement during Holocene period. These structures provide not only more data on the diversity of the deformational features, but also enable to suggest the likely tectonic mechanism responsible for the genesis of these structures, and point to the occurence of seismic events of magnitude Ms≥5 which may have been responsible for the deformation of the Holocene sediments of Rann.