Imaging short‐period seismic radiation from the 27 February 2010 Chile (MW 8.8) earthquake by back‐projection of P, PP, and PKIKP waves

Teleseismic short‐period (0.5–5 s) P waves from the 27 February 2010 Chile earthquake ( M w 8.8) are back projected to the source region to image locations of coherent short‐period seismic wave radiation. Several receiver array configurations are analyzed using different P wave arrivals, including networks of stations in North America ( P ), Japan ( PKIKP ), and Europe ( PP ), as well as a global configuration of stations with a broad azimuthal distribution and longer‐period P waves (5–20 s). Coherent bursts of short‐period radiation from the source are concentrated below the Chilean coastline, along the downdip portion of the megathrust. The short‐period source region expands bilaterally, with significant irregularity in the radiation. Comparison with finite fault slip models inverted from longer‐period seismic waves indicates that the regions of large slip on the megathrust are located updip of the regions of short‐period radiation, a manifestation of frequency‐dependent seismic radiation, similar to observations for the great 2011 Tohoku earthquake ( M w 9.0). Back projection of synthetic P waves generated from the finite fault models demonstrates that if the short‐period energy had radiated with the same space‐time distribution as the long‐period energy, back‐projection analysis would image it in the correct location, updip. We conclude that back‐projection imaging of short‐period signals provides a distinct view of the seismic source that is missed by studies based only on long‐period seismic waves, geodetic data, and/or tsunami observations.