Anatomy of a submarine volcano near Narcondam Island using high-resolution seismic reflection data
Harshad Kumar Srivastav*, Dr. Dibakar GHosal, A. Sai Kumar
Indian Institute of Technology Kanpur
Room no J 109, Hall 7, IIT Kanpur Kanpur, Uttar Pradesh, India Pincode: 208016 Mobile: 7668247911 E-mail: email@example.com
Andaman sea lies in an active tectonic setup where Indo-Australian Plate subducts below the overriding Eurasian plate. This sea results from a three-phase tectonic evolution- extension, extension-rifting, and seafloor spreading between Alcock and Sewell rises during Early to Middle Miocene, separating Burma plate in NW from the Sunda (Eurasia) in SE. A conspicuous volcanic chain passes through the west of the Andaman Sea connects Burma in the north, Narcondam Island, Barren Island, Java in the east, and Sumatra in the south. Narcondam Island is a dormant volcano located East of Andaman Island and is consisted of Dacite-andesite-rhyolite. This submarine volcanic chain and its associated pyroclastic flow fall in a complex tectonic regime influenced by both subduction and seafloor spreading. To date, very few geophysical studies have been carried out close to Narcondam Island to understand its past volcanic activities and associated tectonics. Here, we present a seismic image of a submarine volcano adjacent to Narcondam island using industry-derived high-resolution seismic reflection datasets. We processed a set of E-W trending 2D seismic reflection lines of ~30 km length each, located east of the Narcondam island, in which we first apply bandpass and F-K filtering, followed by parabolic Radon transform to remove noises and seawater multiples, respectively; and then carried out post-stack and pre-stack Kirchhoff time migration followed by a depth conversion. From migrated section of Line 30837, we image an offshore basin enclosed by a cluster of submarine volcanoes in which water depth varies from ~1378-1558 m and sediment thickness varies at CDPs 1032, 2906, and, 4249 as ~0.8, 2.13, and 0.37 km, respectively. From the semblance-based interval velocity, we observe an increase in P-wave velocity from 1.5 km/s near seafloor to ~2.0 km/s at the bottom of the basin deposits, which onlaps to a bathymetric high at the east. A sharp increase in interval velocity to ~6.6 km/s at ~2.4 km depth at CDP 4404 confirms this high as a volcanic origin. We further image a veneer of sediments with a thickness of ~0.1-0.16 km topping the volcano summit and a flow of pyroclastic deposits along the west flank of the volcano.