Browsing by Author "P.N.S. Roy"

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A correlation integral approach to the study of 26 January 2001 Bhuj earthquake, Gujarat, India
(2006) P.N.S. Roy; Avadh Ram
The 26 January 2001 earthquake (ML = 6.9) of Bhuj, Gujarat, India was one of the major natural calamities in recent time for intraplate regions. The spatial distribution of correlation fractal dimension and generalized fractal dimension obtained with the correlation integral approach using 3 years of events (ML ≥ 4) including fifteen foreshocks, mainshock and 155 aftershocks was divided into six consecutive windows to see its temporal variation. The results have revealed that the spatial distribution of correlation fractal dimension and generalized fractal dimension vary in an approximate oscillating pattern in the range 0.90-2. Thus, it may be concluded that the possibility of presence of asperity/barrier is the controlling factor of the level of stress/seismicity or clustering pattern of aftershocks in the region. The Dq spectrum obtained for all the six time windows show a monofractal nature and not a multifractal pattern of the events, which is in a clustered manner for the region. This finding also supports the predominance of an asperity/ barrier model for such a high energy release along the active fault for intraplate regions without heterogeneity in fractal structure or cluster within cluster. © 2005 Elsevier Ltd. All rights reserved.
Fractal dimensions of blocks using a box-counting technique for the 2001 Bhuj earthquake, Gujarat, India
(2005) Avadh Ram; P.N.S. Roy
Several destructive earthquakes have occurred in the Kachchh region of Gujarat during the past two centuries, among them Allah Bund earthquake (M7.8) in 1819, Anjar earthquake (M6) in 1956 and the recent Bhuj earthquake (M7.6) in 2001. The Anjar earthquake was on KMF (Kachchh Mainland Fault) and the recent Bhuj events were caused by a hidden fault north of KMF. The present study discusses the fractal analysis of tectonics governing seismic activity in the region. The region has been divided into five blocks and the fractal dimension of each block has been calculated using the box-counting technique. The results show significantly low value of fractal dimension of the Kachchh rift block consisting of the KMF compared to the other surrounding blocks, which also contain faults and rifts of higher fractal dimension. This indicates that the cause of earthquakes in this block may be asperities and barriers. However, the predominance of aftershocks over foreshocks signifies that barriers may be the main cause. The other results, such as the lower value of dimension of fault clustering show that the Kachchh rift block has faults which are distributed in a clustered manner. In this context, the seismicity of this block seems to be high. © Birkhäuser Verlag, Basel, 2005.
Seismic hazards assessment of Kumaun Himalaya and adjacent region
(2012) P.N.S. Roy; S.K. Mondal; Mallickarjun Joshi
The ongoing continent-continent collision between Indian and Eurasian plates houses a seismic gap in the geologically complex and tectonically active central Himalaya. The seismic gap is characterized by unevenly distributed seismicity. The highly complex geology with equally intricate structural elements of Himalaya offers an almost insurmountable challenge to estimating seismogenic hazard using conventional methods of Physics. Here, we apply integrated unconventional hazard mapping approach of the fractal analysis for the past earthquakes and the box counting fractal dimension of structural elements in order to understand the seismogenesis of the region properly. The study area extends from latitude 28°N-33°N and longitude 76°E-81°E has been divided into twenty-five blocks, and the capacity fractal dimension (D 0) of each block has been calculated using the fractal box counting technique. The study of entire blocks reveal that four blocks are having very low value of D 0 (0. 536, 0. 550, 0. 619 and 0. 678). Among these four blocks two are characterized by intense clustering of earthquakes indicated by low value of correlation fractal dimension (D c) (0. 245, 0. 836 and 0. 946). Further, these two blocks are categorized as highly stressed zones and the remaining two are characterized by intense clustering of structural elements in the study area. Based on the above observations, integrated analysis of the D c of earthquakes and D 0 of structural elements has led to the identification of diagnostic seismic hazard pattern for the four blocks. © 2012 Springer Science+Business Media B.V.