<p>The surface-flattening scheme is a mathematical method that flattens irregular surfaces by transforming Cartesian coordinates into curvilinear ones. However, its application is limited to first arrivals in the context of the topography-dependent eikonal equation (TDEE). Here, we introduce a multi-block surface-flattening scheme that simultaneously transforms Earth’s surface and subsurface interfaces in Cartesian coordinates into horizontal interfaces in curvilinear coordinates, while adaptively adjusting the grid according to the arbitrary geometry of each layer. This scheme allows the recovery of complex seismic velocity structures joint tomographic inversion using multi-type phase arrivals, including converted and reflected waves. Forward modeling is performed using a multi-stage locking sweeping method with high-order finite-difference stencils, in which first arrivals are computed with a factored TDEE solver, and reflected waves are tracked by restarting the TDEE solver from reflective points on an irregular interface. An adjoint-state method formulated in curvilinear coordinates is used to estimate the preconditioned gradient, avoiding both ray tracing and explicit computation of the derivative matrix. Synthetic tests confirm the operability and effectiveness of the proposed approach for imaging complex layered velocity models. Furthermore, we apply the proposed method to wide-angle seismic data acquired in northeastern (NE) Tibetan Plateau, using refracted and reflected arrivals, to image the upper crust. The agreement between the regional tectonic division and the discernible velocity characteristics of the upper crustal structure demonstrates the good resolution achieved with the implemented algorithm.</p>