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

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 Mw≥ 7.0 earthquakes. To address the limited resolution of source spatial extent and rupture expansion velocity (Vr) from teleseismic observations, the events are subdivided into either group 1 (18 events) having independent constraints on Vr from prior studies or group 2 (96 events) lacking independent Vr constraints. For group 2, finite-fault inversions with Vr=2.0, 2.5, and 3.0 km/s are performed. The product Vr ΔσE, with stress drop ΔσE calculated for the slip distribution in the inverted finite-fault models, is very stable for each event across the suite ofmodels considered. It has little trendwithMw, although there is a baseline shift to low values for large tsunami earthquakes. Source centroid time (Tc) and duration (Td), measured from the finite-fault moment rate functions vary systematically with the cube root of seismic moment (M0), independent of assumed Vr. There is no strong dependence on magnitude or Vr for moment-scaled radiated energy (ER/M0) or apparent stress (σa). ΔσE averages ~4MPa, with direct trade-off between Vr and estimated stress drop but little dependence on Mw. Similar behavior is found for radiation efficiency (ηR). We use Vr ΔσE and Tc/M0 1/3 to explore variation of stress drop, Vr 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.