Accretionary tectonics of Burma and the three-dimensional geometry of the Burma subduction zone

The geometry of the Burma Wadati-Benioff zone (WBZ) has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well-located hypocenters. The dip of this surface, which passes through the middle of the WBZ, varies from about 50° in the north near the eastern Himalayan syntaxis to about 30° in the Bay of Bengal area. The eastern edge of the Indo-Burman ranges closely follows the map projection of the 60 km depth contour of the WBZ. The curvature of the Indo-Burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the Indian plate and the leading edge of the overriding Burma platelet. Shallow earthquakes beneath the Indo-Burman ranges are primarily confined to the underthrusting Indian plate. Their focal mechanisms indicate strike-slip faulting and north-south shortening parallel to the eastern margin of the Indian plate. -Authors