A 3D Finite-Element Workflow for Mapping Earthquake Nucleation Tendency Under Tectonic Loading in Embedded Frictional Fault Systems

Abstract Dynamic-rupture simulations commonly prescribe rupture initiation, which complicates assessment of where instability would preferentially localize for a given fault geometry and tectonic loading. We present a 3D finite-element workflow that maps relative nucleation tendency on embedded frictional fault systems without preassigning an initiation point. Faults are represented as frictional contact interfaces within an elastic volume. Gravity is retained in both branches to provide the depth-dependent normal-stress background and stable contact closure on embedded frictional interfaces. The workflow employs paired branches on the same undeformed geometry with an identical mesh: a gravity-only quasi-static baseline and a gravity-plus-tectonic branch that differs only by a small displacement boundary condition. Each quasi-static state is transferred to a short implicit transient analysis on the same undeformed mesh under the same gravity and compatible boundary constraints. Slip may occur through the contact-state transition from sticking to sliding in the transient stage. We define the onset slip s(x) as the slip accumulated over the first N dynamic increments (default N = 1) and use the differential onset slip Δs(x) between the paired branches as a single-event indicator of nucleation tendency. Timestep tests over Δt=0.001–0.05 s identify the same peak node, and 1–2 km meshes give consistent localization at 15–16 km depth; coarser 3–4 km meshes shift the peak to 3–5 km depth, whereas the thresholded high-slip footprint remains resolution dependent.