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

Abstract 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 3 Δ σ E , with stress drop Δ σ 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 ( σ a ). Δ σ 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 3 Δ σ 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.