ANALYSIS OF HARVARD CENTROID-MOMENT TENSOR SOLUTIONS AND COMPUTATION OF STRAIN RATES IN THE HIMALAYA AND TIBETAN PLATEAU REGIONS

Deformation tectonics of the Himalaya and Tibetan plateau regions has been analysed using the Harvard centroid moment tensor data from 1977 to 1996, The slip vectors of the thrust earthquakes in the Himalaya an d the P-axis azimuths of the strike-slip earthquakes in the Tibetan pl ateau region are found to trend NNE on an average, This is in agreemen t with the directions of maximum compression and extension derived fro m the eigen vectors of the summed moment tensor. For the,Himalayan and Tibetan plateau regions, the directions of principal compression are N22 degrees E and N20 degrees E respectively, while the directions of extension are N59 degrees W and N72 degrees W, This indicates that a s imilar compressive regime prevails in both the regions, under the infl uence of the Indian plate motion with respect to the Eurasian plate. T he computed strain rates indicate a crustal thickening in the Himalaya n region, with the ratio of NS convergence, E-W extension and crustal thickening being about 5:2:3; and a crustal thinning in the Tibetan pl ateau region, with the ratio of NS convergence, E-W extension and crus tal thinning being about 4:9:5.