Surendar Kumar

Geodynamics of Burma and Andaman-Nicobar Region, on the basis of tectonic stresses and regional seismicity

Abstract The nature and distribution (in depth and latitude) of earthquakes and deformation in different regions of Burma and Andaman-Nicobar indicate rather unequal horizontal compression and relative movement of different segments. The (east-west) longitudinal distribution of earthquakes delineates well defined zones of seismicity dipping 30–50 degrees from the Andaman trench to a depth of about 180 km under the Andaman Islands. Fault-plane solutions show that the strike slip, normal and thrust faults are associated with seismic and aseismic regions. The change in nature of volcanism from andesite (south) to basalt (north) in Burma suggested that the stress field changed from compressional to tensional. The mechanical coupling, by the deformation of two different segments, caused an extensive contortion of the sediments in the southern Assam massif.

Gravity anomalies, seismicity, subducting slab folding and surface deformations in the orogenic belts—an example from the Andaman-Nicobar region

Abstract Geophysical data in relation to the geometry associated with the Andaman-Nicobar arc are less strongly constrained. The lithosphere, after buckling, becomes convex downwards in a series of plunging ridges (anticlines) and depressions (synclines). The variation of tectonic activity is greater in front of the subducting folded oceanic lithosphere whereas volcanoes are confined to the shear zones present over the common limbs of plunging ridges and depressions. The representation of the subducting slab geometry over the surface leads to tectonic variations in the orogenic belts.

Sandstone dykes in siwalik sandstone-sedimentology and basin analysis-subansiri district (NEFA), Eastern Himalaya

Abstract Sandstone dykes (including sills) of varied thickness and with tapering ends are present either transecting or (sills) parallel to bedding in the Siwalik sandstone of Arunachal Pradesh (NEFA), Eastern Himalaya. The different sedimentary and microstructural analyses show varied conditions of deposition with changing facies from fluvial channel, to alluvial fan, to coastal plain-fan delta. The non-marine and shallow marine environments are indicated by the presence of organised and disorganised gradation and the presence of sandstone dykes in the interface regions. The orientations of the longer axes of the conglomerate along with the sand bedding indicate palaeoflow.

Presence of parallel metamorphic belts in the northwest Himalaya — Reply

Abstract Two types of metamorphics have been reported from the northwestern Himalaya on the basis of characteristic low pressure—high temperature and high pressure—low to high temperature, mineral assemblages.

Intraplate seismicity and geotectonics near the focal area of the Latur earthquake (Maharashtra), India

Abstract The intraplate seismicity of the Latur earthquake of 30th September, 1993 in Peninsular India is characterised by a rather localised earthquake occurrence on the segmented fault lineaments extending in NW-SE, ENE-WSW and NNE-SSW. These fault zones are a zone of weakness which facilitates the faulting process. Remote Sensing, detailed local tectonics, available geophysical and earthquake data have suggested low velocity layers at the depth of 12 ± 3 km which may be due to high temperatures at that depth. The fault splits (splays) developed in the weak zone above the high temperature body may be the cause of the aftershocks. The vertical shaft like feature of the foci of aftershocks and the presence of an aseismic zone suggests that the release of seismic energy is concentrated in the area of Killari by an extensive lower crustal heterogeneity. The stress concentration in the upper crust is induced by the thickening of the lower crust with its ductile behaviour.