SEISMICITY AND REGIONAL TENSIONAL STRESSES IN THE CENTRAL MYANMAR BASIN

Abstract

200km span of crust which includes the Central Myanmar Basinand Central Andaman Basin has been undergoing two tectonic deformations.The first deformation is an NNW–SSE oriented extensional scheme, whichoccurred primarily during the Miocene epoch. The second deformation isa compression during the Pliocene–Pleistocene time. The Burma plate wasflanked by bounding normal faults, which cut the crust into a number ofpieces. This occurred due to the movement of the India plate in the west andthe southward extrusion of the Indochina plate in the east, coupled with thehighly oblique convergence of the India plate beneath the Burma plate. Ductileextension accommodates the development of pull-apart basins and uplifts.A series of pull-apart basins become deposition centers for sediments, anduplifted areas become sediment source areas. Owing to this on-going process,thecrustalblocksarearrayedalongtheboundingfaultsandrotateandtranslatelaterally toward the north. This process accommodates differential verticaland/or horizontal displacement between adjacent basins. In such continentalrift regions, earthquakes occur along or near the border faults and are confinedto the uppermost 12–15km of oceanic crust and 0–50km of continental crust,thus defining the seismogenic layer underneath. In the Central Myanmar Basin,all the historical earthquake records and recent seismic activity from the USGSEarthquake Catalog are generally shallow and are closely related to the normalfaulting and strike-slip faulting formed by extensional deformation. As a result,the Central Myanmar Basin is still under tensional stresses and movementsalong these faults have not yet ceased as indicated by the frequent occurrenceof earthquakes in this area.