Rupture characteristics of major and great (M_w  ≥ 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 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 Vr3ΔσE, with stress drop ΔσE 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 Mw, 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 ~4 MPa, 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 Vr3ΔσE and Tc/M01/3 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.

The 2 March 2016 Wharton Basin Mw 7.8 earthquake: High stress drop north‐south strike‐slip rupture in the diffuse oceanic deformation zone between the Indian and Australian Plates

“…The seismic moment-scaled radiated energy (E R /M 0 ) is~1.25 × 10 À4 , using the finite fault M 0 = 6.06 × 10 20 Nm. The ratio is high relative to typical values, which are less than 3 × 10 À5 for interplate thrust earthquakes [e.g., Ye et al, 2016] and even higher than found for other large strike slip events.…”

“…The source spectrum is enriched in short-period source strength above 0.1 Hz relative to the reference spectrum. Average radiated energy from individual P wave spectra is estimated following the procedure of Venkataraman and Kanamori [2004], and the added contribution from lower frequencies is accounted for as described by Ye et al [2016]. More than 94% of the energy is from frequencies > 0.05 Hz.…”

“…The static stress drop for the main shock is calculated from the slip model in Figure 5 following two procedures discussed in Ye et al [2016]. The first estimate is obtained by eliminating subfaults with seismic moment less than 15% of the peak subfault seismic moment and then using the remaining average slip and slip area in a circular uniform slip calculation; this gives Δσ 0.15 = 15 MPa.…”

Toward automated directivity estimates in earthquake moment tensor inversion

“…Directivity is often discussed using the results of finite fault inversions (Kikuchi & Kanamori 1991;Yue et al 2012;Ye et al 2016) or back-projection techniques (Ishii et al 2005; Koper et al 2011; Directivity moment tensor inversion 1063 Meng et al 2011). Although these methods provide a spatiotemporal history of the rupture process, their application is mainly restricted to large earthquakes.…”

The 2017 Mw 8.2 Chiapas, Mexico, Earthquake: Energetic Slab Detachment

“…3) using linear least square inversion based on Hartzell & Heaton (1983) and Kikuchi & Kanamori (1992), as updated by Ye et al (2016a). We use a planar fault extending asymmetrically toward the northwest, parameterizing each subfault to 10 km along strike and 7.5 km along dip, with a source time function having 14 2-s rise-time triangles offset by 2-s each, allowing up to 30 s subfault durations.…”