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SEISMOTECTONICS AND TECTONIC HISTORY OF THE ANDAMAN SEA

SEISMOTECTONICS AND TECTONIC HISTORY OF THE ANDAMAN SEA. Eguchi, T., Uyeda, S. and Maki, T., 1979 . Earthquake Research Institute, University of Tokyo(Japan) Tectonophysics, 57 (1979) 35-51. INTRODUCTION. The Andaman sea is an active spreading – arc basin.

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SEISMOTECTONICS AND TECTONIC HISTORY OF THE ANDAMAN SEA

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  1. SEISMOTECTONICS AND TECTONIC HISTORY OF THE ANDAMAN SEA Eguchi, T., Uyeda, S. and Maki, T., 1979. Earthquake Research Institute, University of Tokyo(Japan) Tectonophysics, 57 (1979) 35-51

  2. INTRODUCTION • The Andaman sea is an active spreading – arc basin. • In the eastern side of this island the mid-oceanic ridge migrate towards northward the Ninety-East ridge collide with the western end of the old Sunda trench in the middle or late Miocene (10-20 m.y.B.P). • This phenomenon creating a tremendous stress release in the back arc area. • The northward movement of the Indian plate and its collision with Euration plate exert a drag in the back arc region causing the opening of Andaman sea. • This ocean basin formed by a oblique extensional rifting. • In this paper Author examine the seismicity and present tectonism in the Andaman sea region. And he try to correlate the spreading of eastern Indian-ocean and the northward movement of Great India.

  3. Karig 1971 divided back arc basins in to two. • Active marginal basins. • Inactive marginal basins. • Geomorphic and seismic evidences of this area shows that active extension is taken place along the central Andaman(Fitch 1972). • Mid-oceanic ridge migrate towards northward the Ninety-East ridge collide with the western end of the old Sunda trench. • Northward movement of the Indian plate and its collision with Euration plate exert a drag here. Sunda trench

  4. Seismicity From Jan-1964 to Dec-1973 scientist examine the all earthquakes >4.5 between the latitudes 0 ̊N and 20 ̊ N and longitudes 90 ̊ E and 100 ̊ E. • All the epicenters are more in the concave-side of the Andaman arc(fig-1). This may due to the highly oblique subduction of Indian plate in the Andaman sea. • All the epicenters are narrow down to wards the back arc tectonic zone and having a trend of NNE-SSW in the north Andaman sea. This seismic zone playing an important role for the spreading of Andaman sea. • The rectangle showing the central Andaman sea rift valley during the study period a few earthquake occurred in this area (mb4.5) • Deeper earthquake >150km occurred twice in the south during the study period.

  5. The northern Andaman experiencing comparatively shallower earthquake than south Andaman. • Rectangle section from the previous fig, scientist make an E-W-vertical cross section according to the latitudes and the depth of the earthquake.(11̊ N and 13̊ N) • Hear we can able to see the two seismic belts

  6. TECTONIC HISTORY IN THE ANDAMAN SEA • Greater India's northward movement from Australia • Other recent tectonic movement mentioned in the previous part. • From the magnetic anomalies we getting the information about the age of ocean bottom • Eastern part of Ninety east ridge increases southward while that the western part of this ridge increases northward (Sclter and Fisher 1974). • This ridge is the active right lateral transform fault (between 53-32 my) • By (Sclter and Fisher 1974).

  7. On the other hand the Stein and Okla. 1978 suggest small left lateral movement • Any way the models prepared by Tapponnier and Molnar (1975) supposing there was little relative movement either side of the ridge. • For example in the given figure showing the 20 ̊clockwise rotation of the Sumatra around the center of Sunda strait (Point ‘C’). • Spreading might have arrive at the point ‘B’ and at point ‘A’ rotation of Sumatra started(15my). • This process completed at 10 my at this time the spreading of the Andaman sea started.

  8. Conclusion: • The stage that the Andaman sea is appeared in between Burma and west Sumatra as a combined result of ridge subduction and collision with India and Asia • The former and the later collision probability start at about 20-10 and 30-10 m.y. B.P., respectively. • This all theories what ever proposed by the authors in this paper similar to the theory proposed by Alfred Wagner in his classic book “Continental drift”.

  9. Thank you…

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