A decade of short-period earthquake rupture histories from multi-array back-projection

Teleseismic back-projection has emerged as a widely-used tool for understanding the rupture histories of large earthquakes. However, its application often suffers from artifacts related to the receiver array geometry, notably the `swimming' artifact. We present a teleseismic back-projection method with multiple arrays and combined P and pP waveforms. The method is suitable for defining arrays ad-hoc in order to achieve a good azimuthal distribution for most earthquakes.

We present a catalog of short-period rupture histories (0.5-2.0 Hz) containing 54 events from 2010 to 2021 (Mw ≥ 7.5), including recent and significant earthquake ruptures, e.g., 2021 Mw 8.3 South of Sandwich Islands, 2021 Mw 8.2 Chignik, 2021 Mw 8.1 Kermadec Islands, and 2020 Mw 7.8 Simeonof Island.

The method provides semi-automatic estimates of rupture length, directivity, speed, and aspect ratio, which are related to the complexity of large ruptures. We determined short-period rupture length scaling relations that are in good agreement with previously published relations based on estimates of total slip. Rupture speeds were consistently in the sub-Rayleigh regime for thrust and normal earthquakes, whereas strike-slip events propagated in the unstable supershear range. Many of the rupture histories exhibited complex behaviors such as rupture on conjugate faults (e.g., 2018 Mw 7.9 Gulf of Alaska), bilateral ruptures (e.g., 2017 Mw 7.8 Komandorsky Islands), and dynamic triggering by a P wave (e.g., 2016 Mw 7.9 Solomon Islands). For megathrust earthquakes, ruptures encircling asperities were frequently observed, with down-dip (e.g., 2021 Mw 8.1 Kermadec Islands), up-dip (e.g., 2016 Mw 7.8 Pedernales), double encircling (e.g., 2015 Mw 8.3 Illapel), and segmented (e.g., 2020 Mw 7.8 Simeonof Island) patterns. Although there is a preference for short-period emissions to emanate from central and down-dip parts of the megathrust, emissions up-dip of the main asperities are more frequent than suggested by earlier results.