Diagnosing Source Geometrical Complexity of Large Earthquakes

Abstract

We investigated the possible frequency dependence of the moment tensor of large earthquakes by performing W phase inversions using teleseismic data and equally-spaced narrow, overlapping frequency bands. We investigated frequencies from 0.6 to 3.8 mHz. Our focus was on the variation with frequency of the scalar moment, the amount of non-double-couple, and the focal mechanism. We applied this technique to 30 major events in the period 1994–2013 and used the results to detect source complexity. Based on the results, we classed them into three groups according to the variability of the source parameters with frequency: simple, complex and intermediate. Twelve of these events fell into the simple category: Bolivia-1994, Kuril-1994, Sanriku-1994, Antofagasta-1995, Andreanoff-1996, Peru-2001, Sumatra-2004, Sumatra-2005, Tonga-2006, Sumatra-2007, Japan-2011, and the recent Sea of Okhotsk-2013. Seven exhibited significant complexity: Balleny-1998, Sumatra-2000, Indian Ocean-2000, Macquarie Island-2004, Sichuan-2008, and Samoa-2009. The remaining 11 events showed a moderate degree of complexity. Here, we discuss the results of this study in light of independent observations of source complexity, made by various investigators.