scholarly journals Variation of Vp/Vs ratios for granitic layers and weekly average number of earthquakes in NE India

MAUSAM ◽  
2022 ◽  
Vol 53 (4) ◽  
pp. 515-528
Author(s):  
UDAYAN GHOSH
Keyword(s):  
Shillong Plateau ◽  
Ne India ◽  
Phase Data ◽  
Seismic Area ◽  
Granitic Layer

Vp/Vs ratios for the granitic layers in Shillong Plateau and the partially overlapping Tezpur seismic area, have been calculated from Wadati diagrams drawn on the basis of seismic phase data.   From Shillong plateau the average of 23 readings for some months of 1979 for Vp/Vs is found to be 1.71.   For Tezpur area the average of 29 readings of Vp/Vs for 1991-92 is found to be 1.73, but for 1995-96, the average Vp/Vs from 49 readings is found to be 1.68. The overall average from 78 readings for this area is 1.70. The low Vp/Vs for 1995-97 seems to be precursory.   For the granitic layer, taking Vp = 5.92 kms/s and Vp/Vs = 1.70. We get Vs=3.48 km/s for NE India.   Values of Vp/Vs ratios and number of shocks per day are plotted against time and are shown to undergo sudden lowering before many M³4.2 earthquakes. Vp/Vs is generally lowered below 1.60 in such cases.   In Shillong plateau the number of shocks per day for 1979 is found to be three times the number in the adjoining Tezpur area, for 1991-97.

scholarly journals Precise Locating of the Great 1897 Shillong Plateau Earthquake Using Teleseismic and Regional Seismic Phase Data

2021 ◽  
Vol 1 (3) ◽  
pp. 135-144
Author(s):  
Shiba Subedi ◽  
György Hetényi
Keyword(s):  
Seismic Waves ◽  
Active Faults ◽  
Eastern Himalaya ◽  
Great Earthquake ◽  
Shillong Plateau ◽  
Time Data ◽  
Origin Time ◽  
Velocity Models ◽  
Rupture Plane ◽  
Phase Data

Abstract Pinched between the Eastern Himalaya and the Indo-Burman ranges, the Shillong Plateau represents a zone of distributed deformation with numerous visible and buried active faults. In 1897, a great (magnitude 8+) earthquake occurred in the area, and although a subsurface rupture plane has been proposed geodetically, its epicenter remained uncertain. We gathered original arrival time data of seismic waves from this early-instrumental era and combined them with modern, 3D velocity models to constrain the origin time and epicenter of this event, including uncertainties. Our results show that the earthquake has taken place in the northwest part of the plateau, at the junction of the short, surface-rupturing Chedrang fault and the buried Oldham fault (26.0°N, 90.7°E). This latter fault has been proposed earlier based on geodetic data and is long enough to host a great earthquake. Rupture has most likely propagated eastward. Stress change from the 1897 earthquake may have ultimately triggered the 1930 M 7.1 Dhubri earthquake, along a fault connecting the Shillong Plateau with the Himalaya.

scholarly journals Deep geoelectric structure over the Lower Brahmaputra valley and Shillong Plateau, NE India using magnetotellurics

2008 ◽  
Vol 173 (1) ◽  
pp. 92-104 ◽  
Author(s):  
S. G. Gokarn ◽  
G. Gupta ◽  
D. Walia ◽  
S. S. Sanabam ◽  
Nitu Hazarika
Keyword(s):  
Shillong Plateau ◽  
Brahmaputra Valley ◽  
Ne India

scholarly journals Geochemistry of PGE in mafic rocks of east Khasi Hills, Shillong Plateau, NE India

2015 ◽  
Vol 124 (2) ◽  
pp. 459-475 ◽  
Author(s):  
Sampa Hazra ◽  
Jyotisankar Ray ◽  
C Manikyamba ◽  
Abhishek Saha ◽  
S S Sawant
Keyword(s):  
Shillong Plateau ◽  
Mafic Rocks ◽  
Ne India

scholarly journals Soft sediment deformation features in Dauki Fault region: Evidence of paleoearthquakes, Shillong Plateau, NE India

2021 ◽  
Author(s):  
B.V Lakshmi ◽  
Praveen B. Gawali
Keyword(s):  
Urban Areas ◽  
Late Quaternary ◽  
Soft Sediment ◽  
Shillong Plateau ◽  
Deformation Structures ◽  
Regional Deformation ◽  
Ne India ◽  
Deformation Features ◽  
Sediment Deformation ◽  
Soft Sediment Deformation

Abstract The northeastern region (NER) of India has a number of complex regional geological structures, out of which the Dauki fault (DF) is a prominent one. The E-W trending reverse DF, which is referred to go through the southern margin of Shillong Plateau (SP), have played major role in the regional deformation of the adjoining areas and was believed to be active during the Late Quaternary time. Previous paleoseismological studies conducted on the eastern and western part of the DF, Bangladesh, revealed that the fault ruptured in AD 849–920 and AD 1548 respectively. However there were no studies on the DF from southern side of the SP, India. For the first time, from Indian side, soft sediment deformation structures (SSDS) are reported from five trenches in and around the DF zone, SP. Close to the Dauki village, five trenches in the eastern part of the DF, SP, show presence of micro faulting, sand dykes, disturbed strata, and water escape structures. The detailed investigation of SSDS indicates that the origin for deformation is seismic trigger. The 14C AMS dating of deformation structures generated coseismically by earthquakes suggest three seismic events occurred between 130 and 920 year BP, 5415 to 9140 year BP, and at about 4285 year BP. This study confirms that DF is indeed active, at least, since the mid-Holocene. More trenching and dating of seismically induced deformation features are needed to accurately calculate the recurrence interval of major earthquakes that can strike the fast-expanding urban areas in India and Bangladesh.

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