Thisarticlehasbeenacceptedforinclusioninafutureissueofthisjournal.Contentisfinalaspresented,withtheexceptionofpagination. IEEE GEOSCIENCE AND REMOTE SENSING LETTERS 1 Postseismic Ground Deformation Following the September 2010 Darfield, New Zealand, Earthquake From TerraSAR-X, COSMO-SkyMed, and ALOS InSAR Mahdi Motagh, John Beavan, Eric J. Fielding, and Mahmud Haghshenas Abstract —We evaluate early postseismic deformation after the 2010 Darfield, New Zealand, earthquake documented by radar satellite interferometry observations. Applying interferometric techniques to TerraSAR-X, COSMO-SkyMed, and ALOS data, we derive evidence for a variety of coupled solid-fluid postseismic processes after the Darfield event. The contractional jog of the Greendale Fault shows a time-dependent subsidence signal during the first ∼6 months after the event. We detect a dominant subsidence signal in the epicentral area of the Charing Cross fault and also observe a narrow zone (< 15 km) of right-lateral shear along the eastern end of the Greendale Fault, a likely indication of postseismic afterslip process that is operative there after the event. Index Terms—Advanced Land Observing Satellite (ALOS), COSMO-SkyMed (CSK), interferometric synthetic aperture radar (InSAR), postseismic, TerraSAR-X (TSX). I. Introduction T HE Darfield moment magnitude (Mw) 7.1 earthquake occurred on September 4, 2010 04:35 local time in the South Island of New Zealand. Centered in the Canterbury Plains, ∼40 km west of Christchurch and 8 km southeast of Darfield, the mainshock initiated at about 10-km depth, propagated to the surface and extended bilaterally for ∼40 km across alluvial plains west of Christchurch. Significant surface rupture on the previously unrecognized Greendale Fault was reported for the earthquake with predominantly horizontal strike-slip component of up to 5 m and vertical component of up to 1 m [1]. A key seismological and geodetic feature of the Darfield earthquake was its complexity in rupturing multiple fault struc- tures. Seismological observations suggest that the earthquake Manuscript received August 19, 2012; revised January 13, 2013; accepted February 11, 2013. M. Motagh is with Helmholtz Center Potsdam, GFZ German Research Cen- ter for Geosciences, Potsdam 14473, Germany, and also with the Department of Surveying and Geomatics Engineering, University of Tehran, Tehran, Iran (e-mail: motagh@gfz-potsdam.de). J. Beavan is with GNS Science, Lower Hutt, New Zealand (e-mail: j.beavan@gns.cri.nz). E. J. Fielding is with the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA (e-mail: eric.j.fielding@jpl.nasa.gov). M. Haghshenas is with the Department of Surveying and Geomatics Engi- neering, University of Tehran, Tehran, Iran (e-mail: m.haghshenas@ut.ac.ir). Digital Object Identifier 10.1109/LGRS.2013.2251858 Fig. 1. Shaded relief-topography map of the area where the September 2010 Darfield earthquake occurred in the Canterbury Plains of South Island, New Zealand. Rectangles show the area covered by ascending and descending radar scenes used in this letter. The thick, dashed, and dotted lines correspond to TerraSAR-X, Cosmo-SkyMed, and ALOS satellites, respectively. Mapped surface rupture is shown as a thick red line [2]. The yellow star shows the epicenter near Charing Cross (CC). The GeoNet regional moment tensor solution (using regional seismic data prior to the start of strike-slip rupture on the Greendale Fault) and the USGS moment tensor solution (using teleseismic data) are shown by black focal mechanisms on the right side of the figure. started with a reverse faulting at the hypocenter (−43.55°, 172.17°) near Charing Cross (Fig. 1), and continued in a dextral strike-slip sense along the Greendale Fault [2]. This complexity in the main-shock sequence is also evident in geodetic studies that have investigated rupture sources using the inversion of coseismic surface deformation data [3], [4]. In a more recent study, Beavan et al. [6] presented an updated source model for the Darfield earthquake using a combined analysis of GPS and interferometric synthetic aperture radar (InSAR) data. The results show most of the moment release occurred by ∼5 m of right-lateral strike-slip motion on the Greendale Fault. The event also involved rupturing of sev- eral other fault segments, including a blind northeast-striking reverse fault near Charing Cross that initiated the rupture process, a left-lateral fault segment striking north-northwest 1545-598X/$31.00 c  2013 IEEE