B.K. Rastogi

Tectonic Control on Drainage Network Evolution in the Upper Narmada Valley: Implication to Neotectonics

Convergence of the Indian plate towards Eurasia is reflected in neotectonics along several zones throughout the Indian plate. Neotectonics of the upper Narmada river basin following one of the active Son-Narmada Fault (SNF central part) zones in central Peninsular India has been studied through tectonic geomorphometric parameters. The study area is 175 km wide and 400 km long valley and catchment area of upper Narmada river basin in Madhya Pradesh state. High resolution ASTER data indicates neotectonic features like sudden changes in drop of Narmada river floor at two locations around Jabalpur formed by conjugate normal faults. Cross profiles indicate uplift of the entire area by a few hundred meters south of the Son-Narmada south fault. Basin asymmetry parameter indicates northward shifting of the river course from middle of the basin due to uplift of the southern block.

Morphometric evidence of seismicity around Wagad and Gedi Faults, eastern Kachchh, Gujarat

Recent studies suggest that the eastern Kachchh is a potential zone for major earthquakes in the near future. Particularly, the E-W trending faults are considered capable of generating large magnitude earthquakes is further indicated by the recent concentration of the earthquake shocks, which, show two prominent clustering around west and north of the Wagad upland. In view of this, the conventional morphometric analyses of a terrain bounded by the E-W trending North Wagad Fault (NWF) and the Gedi Fault (GF) has been undertaken to ascertain the influence of seismicity in the evolution of the drainage basin. The study suggests that the fifth order drainage basins responded to the seismicity associated with both the NWF and GF. However, compared to the GF, the NWF seems to be more active. In addition to this, based on the stream morphology, we could identify two lineaments trending N-S and E-W. The former appears to be associated with the activity along the Manfara Fault (MF), whereas, the later seems to be the splays of the NWF. Further, a preferential westward shift of the streams suggests left lateral displacement of the E-W trending faults. Overall it can be suggested that the terrain is in juvenile stage implying tectonic instability.

Stress Pulse Migration by Viscoelastic Process for Long-Distance Delayed Triggering of Shocks in Gujarat, India, After the 2001 Mw 7.7 Bhuj Earthquake

Extreme Events an Geophysical Mon

Spatial variations in tectonic activity along the Kachchh Mainland Fault, Kachchh, western India: implications in seismic hazard assessment

Abstract The landscape of Kachchh is a unique example of active intraplate region in the world. Various structural features such as domes, faults, folds and associated intrusive suggest early tertiary tectonic history, while youthful topography like youthful nature of the fault scarps and gorges suggests Quaternary tectonic history. Kachchh Mainland Fault (KMF) is a 170-km-long E–W-oriented south-dipping reverse fault situated in pericratonic Mesozoic rift basin in western India. The KMF is a neotectonically active fault substantiated by distinct tectonic geomorphology and seismotectonic history. As Kachchh region experiences an arid climate, it lacks vegetation and provides favorable conditions for assessing the morphology of mountain fronts and gradient of channels using remote sensing to evaluate the relative tectonic activity. We employed the means of quantitative geomorphic analysis extracted from a DEM to access the spatial variation in tectonic activity. The assessment of geomorphic indicators of active tectonics was carried out using tectono-geomorphic parameters such as stream length-gradient index (SL index), mountain front sinuosity (Smf) and valley floor width–height ratio (Vf). These parameters were combined to generate the relative index of active tectonics (RIAT) which was further divided into four classes as per degree of tectonic activity. The RIAT classes show segmented nature of KMF, with four segments having decrease in degree of tectonic activity from east toward west. The central and the eastern segments of KMF fall in class 1 and class 2 of RIAT, indicating a relatively higher degree of recent tectonic activity undergone by them. The results of geomorphic analysis are consistent with the landforms present, geological setup and seismicity in the study area. The study would be helpful in accessing the regional seismic hazard from KMF for the entire western India.

Response of a dryland fluvial system to climate–tectonic perturbations during the Late Quaternary: Evidence from Rukmawati River basin, Kachchh, western India

Dryland rivers, dominated by short-lived, localised and highly variable flow due to discrete precipitation events, have characteristic preservation potential, which serves as suitable archives towards understanding the climate–tectonic coupling. In the present study, we have investigated the fluvial records of a major, southerly-draining river – the Rukmawati River in the dryland terrain of southern Kachchh, in western India. The sediment records along the bedrock rivers of Kachchh register imprints of the Indian summer monsoon (ISM), which is the major source of moisture to the fluvial system in western India. The Rukmawati River originates from the Katrol Hill Range in the north and flows towards the south, into the Gulf of Kachchh. The field stratigraphy, sedimentology, along with the optical chronology suggests that a braided-meandering system existed during 37 ka period due to an overall strengthened monsoon. A gradual decline in the monsoon strength with fluctuation facilitated the development of a braided channel system between 20 and 15 ka. A renewed phase of strengthened monsoon with seasonality after around 15 ka which persisted until around 11 ka, is implicated in the development of floodplain sequences. Two zones of relatively high bedrock uplift are identified based on the geomorphometry and morphology of the fluvial landform. These zones are located in the vicinity of the North Katrol Hill Fault (NKHF) and South Katrol Hill Fault (SKHF). Geomorphic expression of high bedrock uplift is manifested by the development of beveled bedrock prior to or around 20 ka during weak monsoon. The study suggests that the terrain in the vicinity of NKHF and SKHF is uplifting at around 0.8 and >0.3 mm/a, respectively. Simultaneously, the incision in the Rukmawati River basin, post 11 ka, is ascribed to have occurred due to lowered sea level during the LGM and early Holocene period.

Kappa (κ) model for Kachchh region of Western India

ABSTRACT The empirical factor Kappa (κ), governs the rapid decay of spectral amplitude at high frequencies. It is one of the important parameters required in the simulations of earthquake strong ground motions. The present study estimates κ for 16 sites of Kachchh region of Gujarat (India). The Kachchh region is one of the most seismically active intraplate regions of the world that has experienced shocks of magnitude up to 8.0 in past. We have analyzed 159 accelerograms of 34 earthquakes of magnitude range 3.3–4.9 to estimate the κ. The estimated values of κ vary from 0.016 to 0.045 with an average of 0.023. Our results show no significant dependence of κ on distance (R) for the region. The analysis based on two sites shows that κ0 (κ at R = 0) is lower for the hard rock site (0.016) as compared with the value for the soft rock site (0.0201). One of the important observations of this study is that κ is not the source property for Kachchh region. The estimated values of the κ are useful for the stochastic simulation of earthquake strong ground motions.