Fault Location and Slip Distribution of the 22 February 2011 Mw 6.2 Christchurch, New Zealand, Earthquake from Geodetic Data

The 22 February (local time) MW ∼6.2 Christchurch earthquake occurred within the aftershock region of the 4 September 2010 MW 7.1 Darfield (Canterbury) earthquake (Gledhill et al. 2011). Both the Darfield and Christchurch earthquakes occurred on previously unknown faults in a region of historically low seismicity, but within the zone of plate boundary deformation between the Pacific and Australian plates. The Darfield earthquake caused surface rupture up to 5 m (Quigley et al. 2010, forthcoming), but none has been observed associated with the Christchurch earthquake. Geodetic data indicate that strain has been slowly accumulating within the region (Wallace et al. 2007; Beavan et al. 2002), and the presence of active subsurface faults was known or suspected ( e.g. , Pettinga et al. 2001). Earthquakes of magnitude up to 7.2 in this region had been allowed for in the national seismic hazard model (Stirling et al. 2002), but the observed high apparent stresses (Fry and Gerstenberger 2011, page 833 of this issue) and high ground accelerations (Fry et al. 2011, page 846 of this issue) had not been anticipated, particularly those experienced in the Christchurch event. These and other factors (Fry and Gerstenberger 2011, page 833 of this issue; Fry et al. 2011, page 846 of this issue; Holden 2011, page 783 of this issue), plus the close proximity of the February earthquake to Christchurch city center, were responsible for the major damage caused by the earthquake ( e.g. , Kaiser et al. 2011). A large amount of geodetic ground-displacement data is available to constrain the source of the earthquake, in part because we reoccupied nearly 200 GPS sites that had been observed following the Darfield earthquake, and in part because a number of space agencies collected synthetic aperture radar (SAR) data over …

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