The influence of an active plate boundary on the stress field of the Bhuj tectonics and its analogies with other intraplate earthquakes associated with ancient rift basins have generated interest among the scientific community. A number of hypotheses on the genesis of the 2001 Bhuj earthquake (Mw 7.6) in the peninsular India have already been put forth by several researchers without a common consensus on the issue. Despite no evidence of plate collisional - subduction tectonics and magmatic eruption in the peninsular India the region is being marked with a frequent occurrence of several damaging earthquakes in the rcent past, which has become a great puzzle to the geoscientists. Our aim is to identify the key processes involved in the geneses of the 2001 Bhuj earthquake and its aftershocks within the ancient Kutch rift basin, thereby providing an interpretational framework for three-dimensional (3-D) seismic velocity and Poisson's ratio structures of the source area using high-quality P- and S-wave arrival time data from the best located Bhuj aftershocks using the double difference method of relocating earthquakes. The Bhuj mainshock is located in a distinctive zone, characterized by high P-wave velocity (highVp), low S-velocity (low-Vs) and high Poisson's ratio (high-σ), while areas with high aftershock activity are mainly associated with low Poisson's ratio (low-σ). An integration of the simulated seismotectonic model and existing geo-scientific observations with Vp, Vs and σ tomograms of the source area suggests that a deep-seated intersecting geometry of hidden faults at the base of paleo-rift zone associated with fluid-filled, fractured mafic rock matrix might have contributed to the initiation of the Bhuj earthquake in the intraplate region of western India. The present study infers that the Bhuj mainshock was triggered neither by the north-dipping Kutch mainland nor by the south-dipping North Wagad pre-existing faults. Fluid pressure in the fractured rock matrix at the mainshock hypocentre might have played a key role in the earthquake generating processes, which may have built up differently, possibly in response to dissolution-recrystallisation processes, or thermal processes to initiate the brittle failure in a stable tectonic context by influencing the variations in pore-pressures and thermo-mechanical properties of the continental lithosphere.
|出版ステータス||Published - 2008|
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