Seismotectonics at the terminal ends of the Himalayan Arc

Abstract

The Himalayan arc has an arcuate E-W trending geometry with reversal of trend at the terminal ends -Nanga-Parbat (western) syntaxis and Namcha-Barwa (eastern) syntaxis. Both ends are characterized by an actively deformed uplifted dome with its flanks bounded by active shear zones/faults that cause the majority of the seismicity. Compiled map data and seismo-geological depth sections around these two syntaxial zones have brought out active crustal structure and seismotectonic setup. The Nanga-Parbat syntaxis exhibits upward bending and subsequent thickening of the Indian plate with the cluster of seismicity along the NNE-SSW trending Raikhot fault/Diamer shear in its western margin and a comparatively less active Rupal-Chichi shear zone of N-S trend with diffused seismicity towards the east. The 2005 Kashmir earthquake is spawned due to interaction of the Main Boundary thrust and the Muzaffarabad fault. The Namcha-Barwa syntaxis displays a fault-bounded upliftment and thickening of the Indian plate where Canyon thrust marks the boundary between the Indian and Eurasian plates. The occurrence of the 1950 Assam earthquake in the vicinity of the eastern syntaxis is attributed to a regional right lateral strike-slip motion on the causative fault plane. The seismicity in the syntaxes is primarily controlled by strike-slip faults/shear zones along the flanks of popup antiforms.

Earthquake swarms near eastern Himalayan Syntaxis along Jiali Fault in Tibet: A seismotectonic appraisal

“…These patches may be correlated with mass flowage of mobile rocks and creation of small magmatic pockets by possible decompressional melting. The thickening of the crust is also noteworthy (see sections in Mukhopadhyay et al, 2011) and the exhumation is caused by erosion along the Siang River with crustal scale folding at a rate of w10 mm/yr (Burg et al, 1998). Such zone with extreme horizontal and vertical movement is an ideal candidate for stress accumulation and release and thus characterized by recurrent earthquake swarm activity.…”

“…1) of the eastern Himalayan Syntaxial region (27 e31 N, 92 e99 E) shows the tectonic set up of the area Figure 1. Seismotectonic map of area in and around the eastern Himalaya Syntaxis (compiled after Lee et al, 2003;Mukhopadhyay et al, 2011;Xu et al, 2012) B. Mukhopadhyay, S. Dasgupta / Geoscience Frontiers xxx (2015) 1e8 2 (compiled after Lee et al, 2003;Mukhopadhyay et al, 2011;Xu et al, 2012) with earthquake data (M 4) for the period 1964 to 2011 of reviewed ISC Bulletin. Local seismic network data are not available to the authors.…”

Seismic hazard assessment of Kashmir and Kangra valley region, Western Himalaya, India

“…Seismic activity is related to north-south vergence of Indian and Asian plates. Our previous study (see figure 5(a) of Mukhopadhyay et al 2011b) has also indicated activation of an out-of-sequence (?) thrust west of Gilgit in this segment that is producing the bulk of present seismicity.…”

“…4.0 within time domain 1964-2010) on tectonic elements (after Dasgupta et al 2000) are carried out ( figure 3(a)). The plot and our previous analysis (Mukhopadhyay et al 2011a(Mukhopadhyay et al , 2011b have brought out five distinct seismotectonics zones (A-E of figure 3(a)) where earthquake dominantly clusters -from west to east, they are Kohistan arc (A); Kashmir-Hazara Syntaxis (B); Nanga-Parbat (Western Syntaxis) (C); Karakoram (D) and Himachal Himalaya (E). Further evaluation is carried out through seismo-geological cross sections; which are drawn with earthquake EHB relocated parameters, topography and surface geology to understand the plate configuration in conjunction to the known seismo-tectonic model of the Himalaya.…”

Gas Leakage from Palaeogene Reservoir in Assam - A Geophysical Puzzle

“…The pattern of basin depth variation is usually explained by stronger subduction along the HFT and generation of larger accommodation space [5][6][7] , for fluvial sediment deposition. The northern fringe is closed by the Mishmi Hills, which is in syntaxial relationship 8 with the NPT. The southern fringe is bound by the Mikir Hills which is supposedly the northern extension of Shillong massif 9 .…”