scholarly journals Recent seismic status of Shillong Plateau, Northeast India

BIBECHANA ◽  
2012 ◽  
Vol 9 ◽  
pp. 59-62
Author(s):  
Ananta Panthi ◽  
HN Singh
Keyword(s):  
Temporal Pattern ◽  
Depth Distribution ◽  
Focal Depth ◽  
B Value ◽  
Northeast India ◽  
Great Earthquake ◽  
Shillong Plateau ◽  
Middle Portion ◽  
Strong Activity ◽  
Intermediate Depth

Seismic status of Shillong Plateau of Northeast India has been studied, considering spatial and temporal pattern of the region and using seismicity data for the period 1808-2008. Cutoff magnitude and b-value has been estimated using earthquake data for the period 1963-2008. Seismic activity is observed to be very feeble along the major faults of Shillong Plateau and strong activity is found to occur slightly away from these faults and confined within middle portion at two locations of the region. The temporal pattern shows that the region is due for great earthquake. Focal depth distribution of the events shows that all the events are intermediate depth (less than 70 km). DOI: http://dx.doi.org/10.3126/bibechana.v9i0.7175 BIBECHANA 9 (2013) 59-62

scholarly journals Seismicity Pattern Analysis in and around Shillong Great Earthquake of 1897

2015 ◽  
Vol 5 ◽  
pp. 36-38
Author(s):  
Ananta Panthi ◽  
Jyoti Bhattarai
Keyword(s):  
Depth Distribution ◽  
Focal Depth ◽  
Seismic Energy ◽  
Great Earthquake ◽  
Main Central Thrust ◽  
Seismicity Pattern ◽  
Main Boundary Thrust ◽  
Earthquake Frequency ◽  
Spatio Temporal ◽  
Occurrence Pattern

 The seismicity data of the last 50 years (1963-2012) of the region bounded by 89° - 93° E and 24° -28° N have been analyzed for understanding the seismic characteristics in and around Shillong great earthquake of 1897. The distribution of earthquakes for this period shows sporadic nature of seismic activity in the region. The study of earthquake frequency, the spatio-temporal patterns of seismicity, the focal depth distribution, and the energy release pattern during the period 1963-2012 considering the events with cut-off magnitude (mb ≥ 4.5) have revealed that the region is seismically active. It is observed that most of the seismicity over the Shillong region is associated with the Main Central Thrust, Main Boundary Thrust and Transverse faults. The earthquake occurrence pattern is non-uniform and mostly shallow and intermediate focus in nature. Further, it has been observed that there exists a non-uniform pattern of seismic energy release.The Himalayan Physics Year 5, Vol. 5, Kartik 2071 (Nov 2014)Page: 36-38 

Seismicity, gravity, and tectonics of northeast India and northern Burma

1976 ◽  
Vol 66 (5) ◽  
pp. 1683-1694
Author(s):  
R. K. Verma ◽  
Manoj Mukhopadhyay ◽  
M. S. Ahluwalia
Keyword(s):  
Large Scale ◽  
Bouguer Anomaly ◽  
Northeast India ◽  
Eastern Himalaya ◽  
Basic Material ◽  
Bengal Basin ◽  
Seismic Zone ◽  
Shillong Plateau ◽  
Eurasian Plate ◽  
High Seismicity

abstract Practically the whole of northeastern India and northern Burma is characterized as an anomalous gravity field as well as an area of high seismicity. The Bouguer anomaly in the region varies from +44 mgals over Shillong Plateau to −255 mgals near North Lakhimpur in Assam Valley. Isostatic anomaly (Hayford) varies from +100 to −130 mgals in these areas. Over Arakan-Yoma and the Burmese plains, the isostatic anomalies vary from −20 mgals to −100 mgals. Regions of high seismicity in the area include the eastern Himalaya (including Assam syntaxis), Arakan-Yoma including the folded belt of Tripura, Irrawaddy basin, Shillong Plateau, Dauki fault and the northern part of Bengal basin. The abnormal gravity and seismicity are related to large scale tectonic movements that have taken place in the area mostly during the Cretaceous and Cenozoic times, due to interaction of the Indian, Tibetan, and Burmese plates. The high seismicity indicates that the movements are continuing. The seismic zone underlying Burma is approximately V shaped and dips toward the east underneath Arakan-Yoma. Most of the intermediate-focus earthquakes in Burma underlie the area characterized by negative isostatic anomalies, indicating the probable existence of a subduction zone underneath the Arakan-Yoma and the Burmese plains. The Shillong Plateau has a history of vertical uplift since Cretaceous times. Provided this statement is true, the uplift of the plateau preceded Himalayan tectonics starting 20 to 30 m.y. before continental India made solid contact with the Eurasian plate. The plateau is characterized by large positive isostatic anomalies as well as high seismicity. The positive isostatic anomalies may be due to intrusion or incorporation of basic material from the mantle into the crust underlying the Plateau. These intrusions may have taken place through deep seated faults such as the Dauki and could be responsible for its uplift as well.

scholarly journals Source Parameter of Earthquakes in Talala, Gujarat (India): An Implication towards Seismotectonic

Proceedings ◽  
2019 ◽  
Vol 24 (1) ◽  
pp. 7
Author(s):  
Sandeep Kumar Aggarwal
Keyword(s):  
Epicentral Distance ◽  
Moment Tensor ◽  
Source Parameters ◽  
Focal Depth ◽  
B Value ◽  
Complete Sequence ◽  
P Value ◽  
Centroid Moment Tensor ◽  
North East ◽  
Lateral Plane

Talala is an excellent example of triggered neo-tectonic seismicity between two dams during a monsoon. An earthquake of Mmax 5.1 on 6 November 2007 at 21.16° N; 70.54° E, with a focal depth of 4.5 km and complete sequence, was first-time recorded on the latest broadband sensor. This found a dam/monsoon-induced earthquake preceded by 18 foreshocks of 2 ≤ Mw ≤ 4.8 within 9 h 11 minute, as well as smaller shocks that may not have been recorded because of sparse network coverage. After the deployment of local mobile observatories, aftershocks of Mw ≥ 1.0, which continued for months and subsided to background seismicity after four months, were recorded. The same kind of phenomena repeated, with Mmax 5.0 on 20 October 2011 at 21.06° N; 70.50° E, focal depth 5.5 km, which implies that the potential to generate dam/monsoon-induced seismicity took nearly four years again. These phenomena continued and the sequence was recorded by a network of 10 broadband seismographs (three in the Talala area and seven at an epicentral distance of 30 to 300 km). Centroid Moment Tensor (CMT) solutions and spectral source parameters of mainshock and aftershocks are evaluated to understand the seismotectonic of the region. The CMT depicts a major strike-slip motion along East North East-West South West with a left-lateral plane at 4.5 km depth. This indicates a sympathetic fault extension of the Son-Narmada fault. The source parameters of 400 shocks of Mw 1.0 to 5.1 found seismic moment 1011 to 1016.5 N-m, source radii 120–850 meter, and a stress drop of 0.003 to 25.43 Mpa. The b-value, p-value, fractal dimension, and slip on estimated different faults. The comparison between Talala and Koyna dam-induced source parameters tries to establish a comparison of seismicity from different parts of the world.

Focal depths and source parameters of the Rocky Mountain House earthquake swarm from digital data at Edmonton

1984 ◽  
Vol 21 (10) ◽  
pp. 1105-1113 ◽  
Author(s):  
C. J. Rebollar ◽  
E. R. Kanasewich ◽  
E. Nyland
Keyword(s):  
Epicentral Distance ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Focal Depth ◽  
Rocky Mountain ◽  
Small Variation ◽  
B Value ◽  
Digital Data ◽  
The Difference ◽  
Stress Drops

Seismic records at Edmonton (EDM) and Suffield (SES) between January 1976 and February 1980 show 220 events with magnitudes less than 4 originating near Rocky Mountain House. Many of these events show well defined Sn, Sg, and Pg phases and a small variation in the difference of Sg − Sn and Sg − Pg. Analysis of the theoretical travel times using a structure determined for central Alberta yields an average focal depth of 20 ± 5 km and an average epicentral distance of 175 ± 5 km southwest of Edmonton for 40 of these events. Because Sn was not clear on the remainder, it was not possible to get focal depths for all the events.Seismic moments of 80 events with local magnitudes from 1.6 to 3.5 were found to be in the range of 6.6 ± 2 × 1018 to 7.9 ± 2 × 1020 dyn∙cm (6.6 ± 2 × 1013 to 7.9 ± 2 × 1015 N∙cm). A relationship between local magnitude and seismic moment was log (M0) = 1.3ML + 16.6. This is similar to that determined for California. Source radii, where they could be determined, were 500 ± 50 m and stress drops were 0.75 ± 0.75 bar (75 ± 75 kPa).The energy release of 263 events recorded at EDM from the Rocky Mountain House area was 5.6 × 1017 erg (5.6 × 1010 J). The b value for this earthquake swarm was 0.8, similar to that observed in other parts of western Canada.The depths of focus, the low stress drops, and the statistical similarity to other natural earthquake sequences suggest that at least part of the swarm is of a natural origin.

scholarly journals State of tectonic stress in Shillong Plateau of northeast India

2016 ◽  
Vol 95 ◽  
pp. 36-49 ◽  
Author(s):  
Santanu Baruah ◽  
Saurabh Baruah ◽  
Sowrav Saikia ◽  
Mahesh N. Shrivastava ◽  
Antara Sharma ◽  
...  
Keyword(s):  
Tectonic Stress ◽  
Northeast India ◽  
Shillong Plateau

scholarly journals Seismic b-Value and the Assessment of Ambient Stress in Northeast India

2010 ◽  
Vol 168 (10) ◽  
pp. 1693-1706 ◽  
Author(s):  
Prosanta Kumar Khan ◽  
Manoj Ghosh ◽  
Partha Pratim Chakraborty ◽  
Debdeep Mukherjee
Keyword(s):  
B Value ◽  
Northeast India

Focal depth distribution using sP depth phase and implications for plate coupling in the Hyuganada region, Japan

2006 ◽  
Vol 155 (3-4) ◽  
pp. 219-235 ◽  
Author(s):  
Michitaka Tahara ◽  
Hiroshi Shimizu ◽  
Masao Nakada ◽  
Yoshihiro Ito
Keyword(s):  
Depth Distribution ◽  
Focal Depth ◽  
Plate Coupling

scholarly journals Petrological and geochemical study of the Sylhet trap basalts, Shillong plateau, N.E. India: Implications for petrogenesis

2020 ◽  
Vol 2 (1) ◽  
pp. 01-18
Author(s):  
M. Faruque Hussain ◽  
Md Shofiqul Islam ◽  
Mithun Deb
Keyword(s):  
Partial Melting ◽  
Lithospheric Mantle ◽  
Crustal Contamination ◽  
Northeast India ◽  
Subcontinental Lithospheric Mantle ◽  
Shillong Plateau ◽  
Geochemical Study ◽  
Significant Enrichment

Sylhet Traps exposed along the southern margin of Shillong plateau, Northeast India are subalkaline tholeiitic basalts. The basalts are generally massive but occasionally contain large amygdules of zeolites and chalcedony. Microscopically, some basalts show porphyritic texture with olivine phenocrysts. Phenocryst assemblage of plagioclase ± clinopyroxene ± olivine implies crystallization at shallow level. SEM-EDX analysis shows occurrences of spinel with Ni and Cr within the basalts therefore indicating partial melting of the subcontinental lithospheric mantle as the possible source materials for the basalts. The multi-element plot for the basalts shows two distinct trends: one with significant enrichment of LILE and depletion of HFSE and plot similar to OIB (Type 1) while the other trends are chara cterized by slight enrichment of LILE and negative anomalies at Nb, P and Ti (Type 2). Chondrite-normalized REE patterns for Type 1 basalt shows very high enrichment of LREE and a strong right dip HREE pattern and also plots similar to typical OIB while Type 2 show a slight enrichment of LREE over HREE with small Eu anomaly. The geochemical signatures suggest crustal contamination by plume-derived magma produced by low degree of partial melting for Type 1 basalt. Type 2 basalt was produced by partial melting of subcontinental lithospheric mantle, which may be triggered by plume upwelling.

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.

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