Role of crustal heterogeneity beneath Andaman–Nicobar Islands and its implications for coastal hazard |
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| Authors: | O P Mishra D Zhao Chandan Ghosh Z Wang O P Singh Biman Ghosh K K Mukherjee D K Saha G K Chakrabortty S G Gaonkar |
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| Institution: | (1) Geo-Seismology Division, CGD, Geological Survey of India (CHQ), Kolkata, India;(2) Department of Geophysics, Tohoku University, Sendai, Japan;(3) National Institute of Disaster Management, New Delhi, India;(4) Chengdu Institute of Technology, Chengdu, China;(5) Geodata and Database Division, Geological Survey of India, CHQ, Kolkata, India;(6) SAARC Disaster Management Centre, New Delhi, India |
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| Abstract: | The Andaman–Nicobar (A–N) Islands region has attracted many geo-scientists because of its unique location and complex geotectonic
settings. The recent occurrence of tsunamis due to the megathrust tsunamigenic north Sumatra earthquake (Mw 9.3) with a series
of aftershocks in the A–N region caused severe damage to the coastal regions of India and Indonesia. Several pieces of evidence
suggest that the occurrence of earthquakes in the A–N region is related to its complex geodynamical processes. In this study,
it has been inferred that deep-seated structural heterogeneities related to dehydration of the subducting Indian plate beneath
the Island could have induced the process of brittle failure through crustal weakening to contribute immensely to the coastal
hazard in the region. The present study based on 3-D P-wave tomography of the entire rupture zone of the A–N region using
the aftershocks of the 2004 Sumatra–Andaman earthquake (Mw 9.3) clearly demonstrates the role of crustal heterogeneity in
seismogenesis and in causing the strong shakings and tsunamis. The nature and extent of the imaged crustal heterogeneity beneath
the A–N region may have facilitated the degree of damage and extent of coastal hazards in the region. The 3-D velocity heterogeneities
reflect asperities that manifest what type of seismogenic layers exist beneath the region to dictate the size of earthquakes
and thereby they help to assess the extent of earthquake vulnerability in the coastal regions. The inference of this study
may be used as one of the potential inputs for assessment of seismic vulnerability to the region, which may be considered
for evolving earthquake hazard mitigation model for the coastal areas of the Andaman–Nicobar Islands region. |
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