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 3.0km/s are performed. The product V-r(3)sigma(E), with stress drop sigma(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 V-r for moment-scaled radiated energy (E-R/M-0) or apparent stress (sigma(a)). sigma(E) averages similar to 4MPa, with direct trade-off between V-r and estimated stress drop but little dependence on M-w. Similar behavior is found for radiation efficiency ((R)). We use V-r(3)sigma(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.