Research Page of Abhijit Ghosh
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Non-volcanic tremor is my main focus of research these days. I am working on
non-volcanic tremor at San Andreas Fault and Cascadia Subduction Zone. The broad goal of this
research is to understand the mechanism of non-volcanic tremor, and episodic tremor and slow slip
event, and the physical process(es) that govern(s) it. The figure shows an example of tremor event
at the Parkfield section of San Andreas Fault.
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Earthquake frequency-magnitude distribution (b-value)
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Understanding the earthquake frequency-magnitude distribution, known as
b-value, is my another area of interest. I studied the spatial distribution of b-value
along the subduction interface of the Middle America Trench (MAT), near Nicoya Peninsula, Costa Rica
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We found that spatial b-value mapping can be used to demarcate the zone of strong seismic
coupling along the subduction megathrust. The figure shows the spatial distribution of b
-value along the interface of MAT near Nicoya.
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Earthquake locations and Nicoya catalog
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Earthquake locations are very important for any seismological study. We made a
robust earthquake catalog of Nicoya Peninsula, Costa Rica, that spans from end 1999 to mid 2001
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The seismic network, which consists of 40 land and ocean bottom seismometers, is the part of the
project Costa Rica Seismogenic Zone Experiment. We manually picked ~5000 earthquakes and their
associated phase picks, combines them with the picks done by earlier workers, and relocated them
with simul2000 (previously known as Simulps), using a local velocity model made by
DeShon et al., 2007. This catalog, with ~10000 events, is the most comprehensive earthquake
catalog of MAT, near Nicoya Peninsula, till date. The figure shows earthquake locations from the
Nicoya catalog. Red circles represent earthqukes along the subduction interface, and green circles
are the non-interface events.
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Shallow geophysical exploration
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Shallow resistivity survey can be used for groundwater exploration. Though it is
difficult to use in unconsolidated sediment. We successfully used resistivity methods (vertical
electric sounding) for groundwater exploration at and near the beach area at Sagar Island, West
Bengal, India (Majumdar et al., 2006). Our modeling results suggest a fresh water aquifer of
appreciable thickness at a range of 94 to 174 meters. The figure shows a fence diagram, made from
the resistivity modeling, depicting different lithological layers of the study area.
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I beleive that structural geology is one of the important tools to understand the
tectonism of an area. I studied a structurally complex part of the Sausar Mobile Belt, at Ramtek,
India, that underwent multiple phases of deformation. We found a plunging synform that has the
the evidences of three generations of deformation (Ghosh, 2004). We also found a linear zone of
brecciated rocks that may represents an ancient fault zone. The figure shows the geometry of the
typical folded structure.
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Last updated by Abhijit Ghosh on January 2nd, 2008
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