ACTIVE TECTONICS IN MYANMAR IN RELATION WITH THE LARGE SUMATRA EARTHQUAKE. PRELIMINARY RESULTS OF REPEATED GPS AND MARINE SURVEYS

Myanmar is accommodating the India/Sunda plate oblique motion along a partitioned system including the Sagaing dextral Fault and the northern termination of the Sunda trench. Structural analysis into the field and GPS measurements, combined with marine surveys along the Bengal Basin margin offshore Myanmar were made before and after the last dec.26th Sumatra earthquake. Before the quake, GPS measurements indicate the Sagaing Fault accommodates half of India/Sunda inter-seismic motion, meanwhile the Sunda trench inner wall and the Indo Burmese belt onshore both accommodate other half of this motion within a complex system of incompletely partitioned dextral wrenching. The margin is segmented between rather pure NNE trending dextral shear zones and NW trending shortening zones both spotted with very large submarine landslides probably related to former earthquakes in this region. After the earthquake, northeast decreasing significant co-seismic and post-seismic motion affected GPS stations in southern and central Myanmar, both re-measured three monthes after the quake. Offshore, very recent ruptures in the lower plate were localized at the India/Myanmar international boundary and discrete remobilization of the previously mapped landslides was evidenced northwards along the trench. We think the Sunda trench segment located between Coco Islands and Bangladesh is elastically loaded and could be the source for the next major earthquake in this region.