Investigating Earthquake Cycle Deformation in the Canterbury Region, New Zealand, Using Multi-sensor Satellite Radar Interferometry Observations

Abstract:

In this paper, we summarize distinctive deformation features in the Canterbury region that have been observed using radar interferometry prior to and following the 4 September 2010 Darfield (Canterbury) and 22 February 2011 Christchurch earthquakes.

First, we measured the ground deformation using satellite radar interferometry including 36 Envisat SAR acquisitions in ascending orbits from February, 2004 to July 2010. This dataset shows a subsidence signal over western Christchurch that occurred over a long period of almost 6 years prior to the Christchurch earthquake. The subsidence occurs immediately west of the transition from unconfined to confined aquifers, in an area where the water table is locally deep (exceeding 6 m), unconfined groundwater is downwards flowing and levels are highly variable (van Ballegooy et al. 2014).

Second, two differential interferograms in an ascending orbit between 6 September 2010 and 22 September 2010 and in a descending orbit between 13 September 2010 and 29 September 2010 help us to distinguish between horizontal and vertical components of deformation. In addition, 11 COSMO-SkyMed (CSK) SAR acquisitions in an ascending orbit from October 2010 to February 2011 over the eastern end of the Greendale fault have been processed (Motagh, Beavan et al. 2014). This dataset shows a spectacular time-varying subsidence signal over a previously recognized step-over between the right-lateral eastern and central Greendale faults. A variety of geophysical models, including afterslip and poroelastic rebound have been used to understand the ground deformation. The other feature has also been observed by differential satellite interferometry using TerraSAR-X (TSX) data in a descending orbit between 7 September 2010 and 18 September 2010, following the Darfield earthquake. This dataset shows the ground deformation connecting the eastern end of the Greendale fault towards the city of Christchurch.

Finally, 66 TerraSAR-X (TSX) SAR acquisitions in a descending orbit between February 2011 and April 2014 show approximately three years of postseismic deformation following the Christchurch earthquake. Subsidence signals within the coastal region of Christchurch city and at the end of the eastern Greendale fault are the pronounced anomalies that have been detected.