Building tectonic framework of a blind active fault zone using field and ground-penetrating radar data

Abstract

Blind active faults may lead to earthquake, therefore their identification and characterization constitute an important structural exercise. Such faults can be mapped by high-resolution shallow subsurface geophysical techniques, which offer meter-scale sub-seismic images. The Kachchh Rift Basin (KRB), situated on the western continental edge of the Indian plate, is tectonically active. The KRB is affected by the reactivation of ∼W-striking dip-slip/strike-slip faults. The Kachchh Mainland Fault (KMF) is the largest intra-basinal fault in KRB. The long-term terrain rejuvenation presumably masks the surface expression of the KMF. Shallow subsurface geophysical investigations, assisted by mesoscale structural observations were performed along the western part of the KMF.A ground-penetrating radar (GPR) was used to decipher the sub-seismic position and geometry of KMF. The KMF is inferred to be a near-vertical north-dipping normal fault. GPR data reveal potential colluvial wedges, faulted alluvial and colluvial Quaternary deposits, small-scale horst-graben and off-fault folding, which are not at all apparent in surficial observations and satellite imageries. A sequential evolution of colluvial wedges is explained attributed to KMF reactivation during Cenozoic. The results suggest that the western part of the KMF is tectonically active, and it should not be overlooked despite low seismicity.