The back-projection method uses array processing techniques to image the location and timing of energy release of earthquake sources. Though the basic idea of the method is simple, the necessary data coverage for obtaining useful results only recently became available through the development of large aperture, dense seismic arrays such as the High Sensitivity Seismograph Network in Japan and the Transportable Array in the United States. Since the pioneering work that used the method to investigate the rupture properties of the December 26, 2004 Sumatra-Andaman megathrust event, back-projection has been used in a number of studies, with significant results ranging from the imaging of supershear rupture to dynamic triggering during deep earthquakes.
For this presentation, we focus on the source properties of the recent 2010 Mw 8.8 Maule, Chile and 2011 Mw 9.0 Tohoku, Japan earthquakes. Back-projection results show that these ruptures are extremely complex, with multiple propagation directions and rupture speeds composing each source. In addition, it is shown that the rupture properties of these events can vary considerably when data filtered to different frequency ranges are used in the back-projection analysis. These frequency-dependent changes in rupture behavior are interpreted in terms of the tectonic setting and the source processes that may be acting during the rupture.