Seismotectonics and rates of active crustal deformation in the Burmese arcand adjacent regions

The close vicinity of the Burmese subduction zone to the Himalayan collisio n zone across northeast India produces complex tectonics giving rise to a h igh level of seismicity. Using the hypocentral data of shallow earthquakes (h less than or equal to 70 km) for the period 1897-1995, a large number of focal mechanism solutions and other geophysical data in correlation with m ajor morphotectonic features in the Burmese are and the adjoining areas, we identified 12 broad seismogenic zones of relatively homogeneous deformatio n. Crustal deformation rates have been determined for each one of these sou rces based on summation of moment tensors. The results indicate that along the Kopili-Bomdila fault zone in eastern Himalaya, the deformation is taken up as a compression of 0.12+/-0.01 mm/yr along N16 degrees and an extensio n of 0.05+/-0.004 mm/yr along N104 degrees direction. The deformation veloc ities show a NS compression of 18.9+/-2.5 mm/yr and an EW extension of 17.1 +/-2.2 mm/yr in the Shillong Plateau region, while a compression of 5.4+/-2 .8 mm/yr along N33 degrees is observed in the Tripura fold belt and the Ben gal basin region. The vertical component in the Shillong Plateau shows crus tal thickening of 2.4+/-0.3 mm/yr. The deformation velocities in Indo-Burma n ranges show a compression of 0.19+/-0.02 mm/yr along N11 degrees and an e xtension of 0.17+/-0.01 mm/yr along N101 degrees in the Naga hills region, a compression of 3.3+/-0.4 mm/yr along N20 degrees and an extension of 3.1/-0.36 mm/yr along N110 degrees in the Chin hills region and a compression of 0.21+/-0.3 mm/yr in N20 degrees and an extension of 0.18+/-0.03 mm/yr al ong N110 degrees in the Arakan-Yoma region. The dominance of strike-slip mo tions with the P axis oriented on an average along N17 degrees indicate tha t the Burma platelet may be getting dragged along with the Indian plate and the motion of these two together is accommodated along the Sagaing fault. The velocities estimated along Sagaing transform fault in the back-are regi on suggest that the deformation is taken up as an extension of 29.5 +/- 4.7 mm/yr along N344 degrees and a compression of 12.4 +/- 1.9 mm/yr along N74 degrees in the northern part of the fault zone, and a compression of 17.4/-2.3 mm/yr along N71 degrees and an extension of 59.8 +/- 8.0 mm/yr along N341 degrees in the southern part of the fault zone. The average shear moti on of about 13.7 mm/yr is observed along the Sagaing fault. The deformation observed in the southern part of the syntaxis zone along the Mishmi thrust indicate a compression of 0.63+/-0.08 mm/yr in N58 degrees and an extensio n of 0.6+/-0.07 mm/yr in N328 degrees direction. The region of Shan Plateau , west of Red River fault, shows a compression of 17.7+/-2.6 mm/yr along N3 6 degrees and an extension of 16.1+/-2.4 mm/yr along N126 degrees. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.