A decade of short-period earthquake rupture histories from multi-array
back-projection
Abstract
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) including all 54
earthquakes from 2010 to 2021 with M_w ≥ 7.5 and depth less than 200
km. 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 a tenth of strike-slip events propagated in the
unstable supershear range. Many of the rupture histories exhibited
complex behaviors such as rupture on conjugate faults, bilateral
ruptures, and dynamic triggering by a P wave. For megathrust
earthquakes, ruptures encircling asperities were frequently observed,
with down-dip, up-dip, double encircling, and segmented 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.