Dynamic rupture simulations based on depth-dependent stress accumulation

The depth variation in earthquake rupture behaviour is important for quantitative seismic hazard analysis. We discussed how to set up the initial stress on a fault before an earthquake based on the Mohr–Coulomb criterion considering depth variation. One can assume that the stress is uniformly loaded without exceeding the Coulomb criterion at any depth (stress-constrained condition); however, this implicitly induces a discontinuity of strain in a 1-D layered Earth model. We alternatively assumed that the strain in an upper layer does not exceed that in a lower layer (strain-constrained condition). We numerically demonstrated the dynamic rupture process through 3-D numerical simulations, particularly for the 2019 M w 4.9 Le Teil (France) earthquake, showing a very shallow ruptured area with ground surface displacement. The rupture extent and seismogenic depth can be controlled by a limited layer at depth, which is favourably loaded in advance. The lateral extension of the rupture propagation at this layer is necessary to trigger the above layer but not enough to trigger the layers below. The depth variation of stress loading before an earthquake would be important for assessing the rupture size of moderate (magnitude 5–6) crustal earthquakes in particular.