The Crustal Structure And CTBT Monitoring Of India: New Insights From Deep Seismic Profiling

Abstract : The nation of India has been collecting seismic data for nearly three decades. However, because it has historically been difficult for Western scientists to access this valuable resource or identify individuals responsible for program development, this information has not readily been made available. In the past year (2000), a collaborative effort began between the National Geophysical Research Institute (NGRI) in Hyderabad, India and the US Geological Survey (USGS) in Menlo Park, CA. Since NGRI is a leading organization for geophysics in India, the scope of this collaborative effort will strengthen our knowledge of crustal structure of India. On a continent-wide scale, it was observed that crustal thickness values range from 35 to 40 km in most of India, with the Himalayas being the biggest exception (thickness about 80 km). We have summarized the internal velocity structure of the crust with crustal columns from throughout India. Crustal structure correlates with geological province, and generally thins at the margins, as a result of the transition from continental to oceanic crust. In addition, we have recently reprocessed newly obtained seismic reflection images and interpreted these results with geological and other geophysical constraints. The deep seismic reflection data was acquired using a recording geometry of 100 m shot/detector spacing, utilizing two DFS-V recording units under master-slave mode. Reprocessing was done using ProMax software at the US Geological Survey in Menlo Park, California. Seismic images across the Central Indian Suture Zone reveal a reflection band from 4 to 19 s (twt) that shallows to the SE. A strong reflection band, at 14 s (twt) (approx 44 km) in the northeast, is interpreted as the Moho.