Seasat‐derived gravity constraints on stress and deformation in the northeastern Indian Ocean

We use SEASAT‐derived gravity data to investigate crustal deformation in the NE Indian Ocean. Gravity highs reflecting crustal undulations vary in orientation from E‐W in the Central Indian Basin to NE‐SW in the Wharton Basin. The undulations vary in trend similarly to the variation of the maximum compression directions predicted by a plate driving force model [Cloetingh and Wortel, 1985], and are essentially restricted to the area of predicted compression for both principal horizontal stresses. This agreement implies that the stress model describes the basic features of the deformation observed in the gravity as well as the seismicity. The gravity data also provide insight into two enigmatic tectonic features. The transition in the morphology of the 90°E Ridge at 10°S from a continuous high to a complex blocky structure appears related to the deformation, since undulations in the Central Indian Basin can be projected eastward to blocks on the Ridge. The morphology, formerly interpreted as a fossil feature, may reflect the recent deformation. The discrepancy between the trends of the southernmost 85°E Ridge and the 90°E Ridge, previously thought to exclude similar hot spot track origins, appears to result from treating a crustal undulation as part of the 85°E Ridge. Earthquakes do not appear to be preferentially located with respect to the peaks and troughs of the undulations.