Regional coulomb stress changes and stress triggering mechanisms of the noto MW7.5 earthquake

Abstract

Coulomb stress change (ΔCFS) is widely used to evaluate static earthquake triggering, yet threshold-based triggering statistics can be sensitive to assumptions about fault friction, including possible fluid-related weakening, and to hypocentral uncertainty. Using the 2024 Noto M_W7.5 earthquake sequence, we compute static ΔCFS for (i) the M_W5.5 foreshock acting on the M_W7.5 mainshock receiver plane and (ii) the mainshock acting on early aftershocks within the first 51.5 h. To represent plausible time-varying fault strength potentially influenced by fluids, we convert a friction scenario μ(t) into effective friction μ′(t) under isotropic poroelastic relations for two upper-crustal end members, and evaluate ΔCFS at each aftershock’s reported hypocentral longitude, latitude, and depth. The foreshock yields positive ΔCFS on nodal plane II of the mainshock (~ 0.02 – 0.03 MPa for μ′ = 0.17 – 0.25), exceeding the commonly used 0.01 MPa benchmark. For 2,982 aftershocks, the fractions with ΔCFS ≥ 0.01 MPa are ~ 39 – 46% across four-time windows (ΔCFS ≥ 0.05 MPa: ~ 36 – 44%), while perturbing hypocenters within location uncertainties produces broad 90% intervals (~ 30 – 58%). Sensitivity tests show that the threshold-based triggering fraction increases monotonically with μ′ over 0.20 – 0.80, underscoring the dependence of ΔCFS statistics on frictional assumptions. Deformation and stress calculations indicate hanging-wall uplift and footwall subsidence consistent with reverse faulting, and a heterogeneous horizontal stress field at ~ 10 km depth characterized by NW–SE extension and NE–SW compression. Overall, these results provide a quantitative reference for interpreting ΔCFS-based triggering in the Noto sequence while highlighting key sensitivities in fixed-threshold metrics.