Eastern Bangladesh sits on the seismically active Chittagong-Myanmar fold and thrust belt (CMFB), a north-trending accretionary wedge on the eastern side of the India-Eurasia collision. Earthquakes on the basal décollement and associated thrusts within the CMFB present a hazard to this densely populated region. In this study, we interpret 28 seismic reflection profiles from both published and unpublished sources to constrain the depth of the basal décollement. To convert profiles from the time domain to the depth domain, we integrate sonic log and seismic stacking velocity data to generate time-velocity relationships for different parts of the CMFB. Our analysis reveals that the décollement is ∼9 km deep in northeast and southeast Bangladesh, but shallows to ∼5 km in east-central Bangladesh. The décollement has an area of 7.25 × 10⁴ km² (∼150 × 450 km), making it capable of an Mw 8.5 earthquake. However, the warped geometry of this fault might act as a rupture barrier were a large earthquake to occur on the décollement. Our combined velocity and fault model lay the groundwork for future studies to address seismic segmentation, ground shaking, and rupture modeling in the CMFB. Finally, we use our compiled data set to analyze the evolution of fold kinematics in the CMFB. We observe that folding style and failure mode varies, from mainly ductile deformation in the foreland to mainly brittle in the hinterland. The dual-failure modes within the CMFB support the hypothesis that a region with ductile deformation may still be capable of seismic behavior.

中文翻译：

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孟加拉国东部下陷落的几何形状及其对地震灾害的影响

孟加拉国东部位于地震活跃的吉大港-缅甸褶皱冲断带 (CMFB) 上，CMFB 是印度-欧亚大陆碰撞东侧的一个北向增生楔。CMFB 内基底下降和相关推力的地震对这个人口稠密的地区构成了危险。在这项研究中，我们解释了来自已发表和未发表的来源的 28 个地震反射剖面，以限制基底分离的深度。为了将剖面从时域转换到深度域，我们整合了声波测井和地震叠加速度数据，以生成 CMFB 不同部分的时间-速度关系。我们的分析表明，孟加拉国东北部和东南部的 décollement 深约 9 公里，但在孟加拉国中东部浅至约 5 公里。décollement 的面积为 7.25 × 10⁴  km ² (∼150 × 450 km)，使其能够发生 Mw 8.5 地震。然而，这个断层的扭曲几何形状可能会作为破裂屏障，如果在下层发生大地震。我们的组合速度和断层模型为未来研究 CMFB 中的地震分割、地面震动和破裂建模奠定了基础。最后，我们使用我们编译的数据集来分析 CMFB 中折叠运动学的演变。我们观察到折叠方式和破坏模式各不相同，从前陆以塑性变形为主到腹地以脆性为主。CMFB 内的双重破坏模式支持具有延性变形的区域可能仍具有地震行为的假设。