SIGNIFICANT TRENDS RELATED TO THE SLAB SEISMICITY AND TECTONICS IN THE BURMESE ARC REGION FROM HARVARD CMT SOLUTIONS

A careful examination of 50 centroid-moment tenser (CMT) earthquake fo cal mechanisms in an east-west depth section in the Burmese are region reveals some interesting trends. The P-axis azimuths of most of the m echanisms in the region of the east-dipping Indian lithospheric slab a re, on average, oriented NNE. This indicates that the principal compre ssive stress direction in the Burmese are region is commensurate with the direction of convergence of the Indian plate with respect to the E urasian plate, rather than with respect to the Burmese plate. Another interesting observation is that the strike-slip and thrust type focal mechanisms along the slab do not coexist, but are distinctly segregate d, the predominantly strike-slip type occurring in the upper half of t he slab down to a depth of about 90 km, and the thrust type in the low er half, below that depth level. The former possibly indicates shearin g of the Indian plate past the Burmese plate, along the zone of contac t, which is inferred down to a depth of 90 km. The latter is suggestiv e of a NNE-directed stress on the lower portion of the subducted slab, as it is dragged against the asthenosphere by the Indian plate.