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— The Indo-Burma (Myanmar) subduction boundary is highly oblique to the direction of relative velocity of the Indian tectonic plate with respect to the Eurasian plate. The area includes features of active subduction zones such as a Wadati-Benioff zone of earthquakes, a magmatic arc, thrust and fold belts. It also has features of oblique subduction such as: an arc-parallel strike-slip fault (Sagaing Fault) that takes up a large fraction of the northward component of motion and a buttress (the Mishmi block) that resists the motion of the fore-arc sliver. In this paper, I have examined the seismicity, slip vectors and principal axes of the focal mechanisms of the earthquakes to look for features of active subduction zones and for evidence of slip partitioning as observed in other subduction zones. The data set consists of Harvard CMT solutions of 89 earthquakes (1977–1999 with 4.8≦̸Mw≦̸7.2 and depths between 3–140 km). Most of these events are shallow and intermediate depth events occurring within the Indian plate subducting eastward beneath the Indo-Burman ranges. Some shallow events within the fore-arc region have arc-parallel Paxes, reflecting buttressing of the fore-arc sliver at its leading edge. Some of the shallowest events have nearly E-W oriented P axes which might account for recent folding and thrusting. Examination of earthquake slip vectors in this region shows that the slip vector azimuths of earthquakes in the region between 20°–26°N are rotated towards the trench normal, which is an indication of partial partitioning of the oblique convergence. It is seen that all aspects of seismicity, including the paucity of shallow underthrusting earthquakes and the orientation of P axes, are consistent with oblique convergence. The conclusions of this paper are consistent with recent geological studies and interpretations such as the coexistence of eastward subduction, volcanic activity and transcurrent movement through mid-Miocene to Quaternary period. [ABSTRACT FROM AUTHOR]

We present a modern seismological study of the earthquake of 26 June 1941 in the Andaman Islands, the largest pre-2004 event along that section of the India-Burma plate boundary. Despite a large conventional magnitude ( M PAS = 8.1 ), it generated at best a mediocre tsunami for which no definitive quantitative reports are available. We show that the 1941 earthquake took place under the Andaman accretionary prism and consisted of a composite event, whose nucleating phase had a strike-slip mechanism incompatible with a data set of spectral amplitudes of mantle Rayleigh and Love waves. Combining this initial phase with a larger normal faulting mechanism can reconcile them with P-wave first motions, reports of subsidence on the eastern coast of the Andaman Islands and the small amplitudes of any putative tsunami. The small tsunami results from a combination of that mechanism and of a source located under the islands themselves and in shallow water, implying a reduction in amplitude under Green's law when transitioning to a deeper basin. [ABSTRACT FROM AUTHOR]