Statistical analysis of the 2010 M W 7.1 Darfield Earthquake aftershock sequence

Abstract

Statistical properties of the aftershock sequence of the M W 7.1 Darfield (Canterbury, New Zealand) earthquake are studied. The sequence exhibits rich scaling behaviour in magnitude and aftershock decay rates. In particular, we observe a marked variability in the frequency-magnitude statistics in space, between early and late times after the mainshock and over different magnitude ranges. The mainshock triggered two large earthquakes (22 February 2011 M W 6.2 Christchurch earthquake and 13 June 2011 M W 6.0 earthquake) that occurred later in the sequence and generated their own aftershock sequences. The frequency-magnitude statistics of the sequences are modelled using the Gutenberg–Richter scaling relation. We also study the difference between the magnitudes of the largest recorded aftershocks and the mainshock. This is analysed and discussed using the modified Båth law. In this context we consider the M W 6.2 Christchurch and 13 June 2011 M W 6.0 earthquakes as the largest aftershocks of the Darfield mainshock. It is also observed that the aftershock decay rates can be approximated by the modified Omori law. The obtained results indicate that the aftershock sequence exhibits self-similarity in both magnitude and time.