Splitting function measurements for Earth's longest period normal modes using recent large earthquakes

Abstract

Recent megathrust earthquakes, such as the 23 June 2001 Peru event, the Sumatra events of 2004 and 2005 and the 27 February 2010 Chile event, have given us the opportunity to measure splitting of the longest period normal modes. We use wave spectra to make robust measurements for modes 0 S 2, 0 S 3, 0 S 4, 2 S 1 and 1 S 2. Singlet frequencies of these modes have been measured previously using gravimeters, but here we use seismic records to observe splitting functions for 0 S 2 and 2 S 1 for the first time. Cross-coupling with nearby modes is included to account for ellipticity and rotation of the Earth and results in significantly improved splitting function measurements for 0 S 3, 0 S 4 and 1 S 2 compared with previous studies. The new splitting function measurements can easily be implemented in future tomographic modelling of aspherical velocity and, particularly, density structure. Copyright © 2011 by the American Geophysical Union.