Rupture characteristics of major and great (M_w  ≥ 7.0) megathrust earthquakes from 1990 to 2015: 1. Source parameter scaling relationships

摘要

Source parameter scaling for major and great thrust-faulting events on circum-Pacific megathrusts is examined using uniformly processed finite-fault inversions and radiated energy estimates for 114 M_w ≥ 7.0 earthquakes. To address the limited resolution of source spatial extent and rupture expansion velocity (V_r) from teleseismic observations, the events are subdivided into either group 1 (18 events) having independent constraints on V_r from prior studies or group 2 (96 events) lacking independent V_r constraints. For group 2, finite-fault inversions with V_r = 2.0, 2.5, and 3.0 km/s are performed. The product V_r^3Δσ_E, with stress drop Δσ_E calculated for the slip distribution in the inverted finite-fault models, is very stable for each event across the suite of models considered. It has little trend with M_w, although there is a baseline shift to low values for large tsunami earthquakes. Source centroid time (T_c) and duration (T_d), measured from the finite-fault moment rate functions vary systematically with the cube root of seismic moment (M_0), independent of assumed V_r. There is no strong dependence on magnitude or Vr for moment-scaled radiated energy (E_R/M_0) or apparent stress (σ_a). Δσ_E averages ~4 MPa, with direct trade-off between V_r and estimated stress drop but little dependence on M_w. Similar behavior is found for radiation efficiency (η_R). We use V_r^3Δσ_E and T_c/M_0^(1/3) to explore variation of stress drop, V_r and radiation efficiency, along with finite-source geometrical factors. Radiation efficiency tends to decrease with average slip for these very large events, and fracture energy increases steadily with slip.