Gaurav D. Chauhan

By Girish Ch Kothyari, Ajay P. Singh, Sneha Mishra, Raj Sunil Kandregula, Indu Chaudhary and Gaurav Chauhan

The eastern part of Kachchh Rift basin was reactivated after 2001 Bhuj earthquake of Mw 7.7 and continuous seismicity has been recorded since then. The northern part of Wagad upland also experienced moderate earthquakes Mw ≥ 5.7 in February 2006 and March 2007. These moderate to major Intraplate earthquakes provide a unique opportunity to study the effects and linkage between brittle-ductile dynamics, surface processes and drainage evolution. We presented a geomorphological analysis of the Wagad highland providing new constraints on the evolution of river network. The shallow to deeper nature of fault and their response to development of hydrological networks has been analyzed using seismic tomography. Based on surface drainage offset and seismic structures several E-W oriented faults controlling fluvial dynamics are identified. From seismic structures and drainage offset it is clear that the fluvial dynamics is controlled by shallower to deeper faults. The estimated attributes are well supported with seismic structures and focal mechanisms solutions. Based on fluvial offset and seismic structure analysis a new tectonic model has been proposed for WH. The tectonic model shows that the faults WH are well connected at deeper level and generated negative flower structures and significantly controlling surface fluvial dynamics.

Part of the book: Tectonics

By Sanjib K. Biswas and Gaurav D. Chauhan

The tectonic framework of the Indian Plate started to evolve since the break-up of Gondwanaland in the Late Triassic. It evolved mainly during the time between its separation from the African plate in the Early-Cretaceous and its collision with the Eurasian plate on the north in Late-Middle Eocene and with the Burmese plate in the northeast in Late-Oligocene. Present active tectonic zones, responsible for earthquake generation, were created by the collision pattern and subsequent plate motion. Continued subduction and plate motion due to ridge push and slab pull are responsible for the activation of primordial faults in the inherent structural fabric of the craton depending on the related stress field. Major tectonic zones of the Indian continental plate are related to the collision fronts and the reactivated intra-cratonic faults along the resurgent paleo-sutures between the proto-cratons. Major Tectonic Zones (TZ) are Himalayan TZ, Assam-Arakan TZ, Baluchistan- Karakoram TZ, Andaman-Nicobar TZ, and Stable Continental Region (SCR) earthquake zone. The structure of the continental margins developed during the break-up of Gondwana continental fragments. Western margin evolved during the sequential separation of Africa, Madagascar, and Seychelles since the Late-Triassic to Late Cretaceous time. The Eastern margin structure evolved during the separation of Antarctica in Mid Cretaceous. The orogenic belt circumscribing the northern margin of Indian plate is highly tectonised as the subduction of the plate continues due to northerly push from the Carlsberg Ridge in the SW and slab-pull towards northeast and east along the orogenic and island arc fronts in the NE. This stress pattern induced an anticlockwise rotatory plate motion. The back thrust from the collision front in the direction opposite to the ridge push put the plate under an overall compressive stress. This stress pattern and the plate motion are responsible for the reactivation of the major intra-cratonic faults. While the tectonised orogenic belts are the zones for earthquake nucleation, the reactivated faults are also the strained mega shear zones across the plate for earthquake generation in SCR. These faults trending WNW-ESE are apparently the transform faults that extend across the continent from Carlsberg ridge in the west to the collision zones in the northeast. As such, they are described here as the ‘trans-continental transform faults’. Three such major fault zones from north to south are (i) North Kathiawar fault - Great Boundary fault (along the Aravalli belt) zone, (ii) South Saurashtra fault (extension of Narmada fault) – SONATA-Dauki-Naga fault zone, and (iii) Tellichery-Cauvery-Eastern Ghat-T3-Hail Hakalula-Naga thrust zone. All these trans-continental faults, which are mega-shear zones, are traceable from western offshore to the northeastern orogenic belts along mega tectonic lineaments across the continent. The neotectonic movements along these faults, their relative motion, and displacement are the architect of the present geomorphic pattern and shape of the Indian craton. The overall compressive stress is responsible for strain build-up within these fault zones and consequent earthquake nucleation. The mid-continental Sonata-Dauki shear zone follows the Central Indian Suture Zone between Bundelkhand Proto Continent (BPC) and Deccan Proto Continent (DPC). With the reactivation of this shear zone, the two proto-cratonic blocks are subjected to relative movement as the plate rotates anticlockwise. The kinematics of these movements and their implications are discussed here with a special reference to the recent 2001 Bhuj earthquake.

Part of the book: Sedimentary Rocks and Aquifers