We present an improved 3-D shear wave velocity image of the uppermost mantle beneath the Bay of Bengal (BoB), the Bengal basin and the adjoining Indian shield to their west. Shear wave velocities were inverted from fundamental mode Rayleigh wave group velocities calculated along 21,600 crisscrossing paths from cross correlation of ambient noise as well earthquake seismograms. This study shows the hitherto unsuspected existence of distinct lithospheres in the eastern and western Bay of Bengal, on either side of 86^° E longitude, but understandable in terms of their different origins and ages. The western Bay of Bengal, with greater than 120 km thick layered lithosphere has a shear wave velocity of 4.7 km/s beyond the depth of 90 km. This velocity structure is in lateral continuation with the high velocity in the adjacent cratonic India. The lithosphere thickening can be explained to be the result of conductive cooling of an oceanic plate with a temperature of 1300 ± 50 °C at its base. The remarkable similarity between the velocity structure of the western BoB and the adjoining Indian craton, which could be fortuitous, however, suggests the untested possibility that the fracture plane mediating the initial break-up of India from Antarctica might have been inclined towards the former creating asymmetrically spreading oceanic crust over a cratonic upper mantle. The eastern Bay of Bengal (BoB), in contrast, has thinner lithosphere (60–75 km) with minimum velocity of ~4.2 km/s which is anomalously low for an old ocean. This significant thinning could have been caused by a number of factors such as reheating of the original lithosphere arising from a thermal boundary layer instability or westward flow of mantle due to slab rollback of subducting Indian lithosphere in the Andaman arc.

我们提供了孟加拉湾（BoB），孟加拉盆地和其西部相邻的印度盾下方最上层地幔的改进的3-D剪切波速度图像。剪切波速度是从基本模式瑞利波群速度反转的，基波瑞利波群速度是根据环境噪声和地震地震图的互相关性沿着21,600个交叉路径计算得出的。这项研究表明，迄今为止，在孟加拉国东部和西部，在86 ^°的两侧，都存在不同岩石圈的迄今未曾预料到的存在。经度，但根据其不同的来历和年龄可以理解。孟加拉湾西部，层状岩石圈厚度超过120 km，超过90 km的深度，其剪切波速度为4.7 km / s。这种速度结构在相邻的克拉通印度以高速度横向连续。岩石圈增厚可以解释为是对基底温度为1300±50°C的大洋板进行传导冷却的结果。西方BoB的速度结构与毗邻的印度克拉通之间的惊人相似性（这可能是偶然的）表明，介导印度从南极洲初始解体的断裂面可能倾向于前者的形成，这一未经检验的可能性在克拉通上地幔上不对称地散布着洋壳。相反，孟加拉湾东部（BoB）的岩石圈较薄（60–75 km），最小速度为〜4.2 km / s，对于一个古老的海洋来说反常较低。这种显着的变薄可能是由许多因素引起的，例如由于热边界层的不稳定性或安达曼弧中俯冲的印度岩石圈的平板回滚所致的地幔向西流动，从而引起了原始岩石圈的再加热。