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Tectonic control on the drainage system in a piedmont region in tectonically active eastern Himalayas

Frontiers of Earth Science 2012年第1期6卷 29-38页

作者： Chandreyee GOSWAMI dhruba mukhopadhyay Bikash Chandra PODDAR Asutosh College Saltlake CityKolkata 700026India Raman Center for Applied and Interdisciplinary Sciences Saltlake CityKolkata 700075India BE 267 Saltlake CityKolkata 700064India

The impact ofneotectonic activity on drainage system has been studied in a large alluvial fan in the eastern Himalayan piedmont area between the Mal River and the Murti River. Two distinct E-W lineaments passing through this area had been identified by Nakata （1972, 1989） as active faults. The northern lineament manifested as Matiali scarp and the southern one manifested as Chalsa scarp represent the ramp anticlines over two blind faults, probably the Main Boundary Thrust （MBT） and the Himalayan Frontal Thrust （HFT）, respectively. The fan surface is folded into two antiforms with a synform in between. These folds are interpreted as fault propagation folds over the two north dipping blind thrusts. Two lineaments trending NNE-SSW and nearly N-S, respec- tively, are identified, and parts of present day courses of the Murti and Neora Rivers follow them. These lineaments are named as Murti and Neora lineaments and are interpreted to represent a conjugate set of normal faults. The rivers have changed their courses by the influence of these normal faults along the Murti and Neora lineaments and their profiles show knick points where they cross E-W thrusts. The overall drainage pattern is changed from radial pattern in north of the Matiali scarp to a subparallel one in south due to these conjugate normal faults. The interfluve area between these two rivers is uplifted as a result of vertical movements on the above mentioned faults. Four major terraces and some minor terraces are present along the major river valleys and these are formed due to episodic upliftment of the ground and subsequent down- cutting of the rivers. The uppermost terrace shows a northerly slope north of the Chalsa scarp as a result of folding mentioned above. But rivers on this terrace form incised channels keeping their flow southerly suggestingthat they are antecedent to the folding and their downcutting kept pace with the tectonism.

关键词： alluvial fan drainage pattern thrust normalfault active tectonic

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Kinematics of faults in Bengal Basin:Constraints from GPS measurements

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Geodesy and Geodynamics 2020年第4期11卷 242-251页

作者： Mallika Mullick dhruba mukhopadhyay Raman Centre for Applied and Interdisciplinary Sciences 16AJheel RoadKolkata700075India

The crustal deformation of Bengal Basin is constrained by motion on faults within the basin and those along the basin boundaries on all sides except the southern *** Hinge Zone(EHZ),the most prominent structure within Bengal Basin,running through Kolkata-Ranaghat-Mymensingh,shows present day reactivation by hosting 8 earthquakes of magnitude 5.3 to 7.2 on or near its vicinity since *** of GPS derived velocities of stations around the hinge belt reveals a change in crustal kinematics across the *** predicted fault model that best fits the observed GPS station velocities on the surface shows that EHZ is a low angle east dipping fault which is locked to a depth of 10 km below the alluvium cover with a maximum slip rate deficit of 1.6±0.7 mm/yr in its northern part at a shallow depth from surface while the deficit in the southern part of EHZ is 1.0±0.6 mm/*** Garh-Moyna Khandaghosh fault running almost parallel to the western basin-shield margin does not show significant slip rate *** basin-bounding faults are more active than the faults within and therefore they are greater sources of seismic hazard in the *** model results reveal that the Sylhet trough region in the northeastern corner is most vulnerable to future earthquakes as it undergoes deformation due to a maximum slip rate deficit of 9.5±2.4 mm/yr on the shallowly dipping locked megathrust along the eastern margin of the basin plus that of 7.4±2.6 mm/yr on the over thrusting Dapsi thrust and Dauki fault in the north.

关键词： Bengal basin Active faults GPS Slip rate deficit Coupling fraction

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Quantitative analysis of the Nepal earthquake on 25 April, 2015 in the perspective of future earthquake hazard

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Geodesy and Geodynamics 2017年第2期8卷 77-83页

作者： Mallika Mullick dhruba mukhopadhyay Raman Centre for Applied and Interdisciplinary Sciences 16A Jheel Road Kolkata 700075 India

The earthquake that occurred in Nepal on 25 April, 2015 was followed by about 256 aftershocks which continued for another 20-25 days. The Coulomb stress change due to the main shock has been estimated at depths 10 km, 15 km and 22 km which justify the occurrence of about 218 aftershocks of magnitudes 4 to 5 mostly at 10 km depth and the rest of magnitudes 5 to 7.3 mostly at 15-30 km depth. The western, southern and northern fringes of the fault plane that slipped on 25 April, 2015 show a high value of positive Coulomb stress change estimated at the above mentioned depths and yet these parts of the fault remained devoid of any aftershock epicentre and therefore must be treated as seats for possible future events. Co-seismic displacement of 5 GPS stations located in Nepal after the devastating earthquake of MwZ8 on 25 April, 2015 and its largest aftershock of MwZ3 on 12 May, 2015 have been separately estimated and analysed.

关键词： Nepal Himalaya Aftershock Positive Coulomb stress change Co-seismic displacement Future earthquake

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