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

Abstract

Teleseismic short-period (0.5-5s) P waves from the 27 February 2010 Chile earthquake (Mw 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 (5-20s). 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. Copyright 2012 by the American Geophysical Union.