Kinematic Source Model of the 22 February 2011 Mw 6.2 Christchurch Earthquake Using Strong Motion Data

Abstract

The Canterbury earthquake sequence began in September 2010 with the Mw 7.1 (source: GeoNet catalog, http://geonet.org.nz/canterbury-quakes/) Darfield earthquake that ruptured the previously unknown 40-km-long Greendale fault 30 km west of Christchurch (Gledhill et al. 2011). Extreme ground accelerations as high as 1.8 g near the epicenter were recorded. The event caused intense liquefaction in the eastern suburbs of Christchurch as well as closer to downtown, near the course of the Avon River. The Darfield earthquake was followed by a major aftershock on 22 February local time (21 February UTC) of magnitude Mw 6.2 (source: GeoNet), but Me 6.7 (source: USGS, http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usb0001igm/neic\_b0001igm\_e.php). This earthquake was centred only a few kilometers south of the Christchurch city center. Extremely high accelerations (as high as 2.2 g) were also recorded near the epicenter (Kaiser, Benites et al. 2011). In addition to the extreme liquefaction seen after the Darfield earthquake, this event also caused landslides, large rockfalls, widespread damage to earthquake-risk buildings in Christchurch, and, most tragically, about 180 casualties. Another large aftershock of Mw 6.0 (source: GeoNet), but with Me 6.7 (source: USGS), subsequently occurred on 13 June local time (12 June UTC) just a few kilometers south of the February event, causing further damage, landslides, rockfalls, and liquefaction. Following the Darfield earthquake, the GeoNet network (New Zealand National Hazard Monitoring Network) and its regional component the CanNet network (Berrill et al. 2011) was supplemented by the deployment of 13 additional strong motion instruments regionally (and another nine following the February earthquake). We used this dense network of strong motion instruments to constrain the source kinematics of the February event. We present the inversion scheme and discuss its limitations. These results are preliminary, since more thorough data processing is needed; however, they already provide a key model that will help in understanding the sequence …