The Darfield moment magnitude (Mw) 7.1 earthquake of September 2010 is the first heavily damaging earthquake to strike New Zealand since the surface wave magnitude (MS) 7.8 Hawkes Bay earthquake in 1931. Although the earthquake has a clear strike-slip surface expression characterised by the Greendale Fault, seismological evidence suggests it is a complex event beginning as a reverse faulting earthquake. Evidence for complexity of the mainshock includes a well constrained epicentre north of the surface fault trace, high near-source vertical accelerations, first-motion and regional moment tensor focal mechanisms which differ from teleseismic solutions, and a complex aftershock pattern. The earthquake and aftershock sequence were very well recorded by the GeoNet sensor networks in the region, and provide an exceptional dataset for understanding the earthquake rupture process and reducing damage from future earthquakes. This was the most significant test of GeoNet since its inception in 2001, and the first such New Zealand event in the “internet age”. GeoNet data proved important for the response and the interaction with emergency management, media and the public. The GeoNet website sustained continued heavy load over the weeks and months following the earthquake but continued to deliver timely information because of significant improvements carried out as the aftershock sequence continued.