Evaluating the seismic hazard in the Kachchh Region, western India using the river gradient length anomaly technique
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Ó Indian Academy of Sciences (0123456789().,-volV)(0123456789( ).,-volV)
Evaluating the seismic hazard in the Kachchh Region, western India using the river gradient length anomaly technique RAJ SUNIL KANDREGULA1,3,* , GIRISH CH KOTHYARI1, GAURAV CHAUHAN2, VASU PANCHOLI1, K V SWAMY3, ABHISHEK LAKHOTE2, SNEHA MISHRA1 and M G THAKKAR2 1 Department 2 Department 3
of Active Tectonics, Institute of Seismological Research, Gandhinagar, Gujarat, India. of Earth and Environmental Science, K S K V Kachchh University, Bhuj, Gujarat, India. Department of Geology, Adikavi Nannaya University, Rajahmundry, Andhra Pradesh, India. *Corresponding author. e-mail: [email protected] MS received 27 December 2019; revised 12 April 2020; accepted 26 May 2020
In the present study, we assess seismic hazard potential and surface deformation pattern along and across the strike of major active faults in the intra-plate Kachchh Rift Basin (KRB). Towards this, we adopted river Gradient Length Anomaly (GLA) technique, which detects recent tectonic deformation along a river proBle on local and regional scales. The major deviations along the river proBle can be correlated with exogenic (erosion/sedimentation/anthropogenic) and endogenic (active tectonic movement) processes. We analysed 130 river proBles for GL anomalies, over an area of *26,700 km2 in the KRB to identify possible locations that have undergone active tectonic deformation associated with the fault movement. The acquired results show that the higher magnitude negative GL anomalies (uplift) are observed proximal to the fault zones. Our estimates reveal that, around 13% of the study area falls under high tectonically active zone, around 27% of the area falls under moderately active zone, while 60% of the area shows very low or negligible tectonic activity. The estimated results of the GL anomalies are compared with the existing double-difference tomograms, to understand the role of subsurface fault dynamics on the GL anomalies. Furthermore, the results of GLA are correlated with the existing results of the peak ground acceleration (PGA) values of the basin, in order to obtain the precise information regarding surface deformation and site-speciBc ground acceleration for accurate assessment of seismic hazard. Keywords. Gradient length anomaly; seismic hazard; tectonic geomorphology; Kachchh; western India.
1. Introduction The seismically active, E–W oriented intra-plate Kachchh Rift Basin (KRB) in western India is structurally bordered by Nagar Parkar Fault (NPF) and the North Kathiawad Fault (NKF) (Biswas 1982, 2016; Bgure 1). The KRB formed during Late Triassic to Early Jurassic with the rifting of Eastern
Gondwana land and started expanding from north to south as the Indian plate drifted in anticlockwise manner towards the Eurasian plate (Biswas 2005, 2016). The geometry of pre-existing antecedent normal faults was changed into strike-slip faults with a divergent oblique-slip component because of the horizontal shear stress (Biswas 2005, 2016). Some of these faults are Island Be
