The M_w6.2 Christchurch earthquake of February 2011: preliminary report

Abstract

A moment magnitude (M w) 6.2 earthquake struck beneath the outer suburbs of Christchurch, New Zealand's second largest city, on 22 February 2011 local time. The Christchurch earthquake was the deadliest in New Zealand since the 1931 M w 7.8 Hawkes Bay earthquake and the most expensive in New Zealand's recorded history. The effects of the earthquake on the region's population and infrastructure were severe including 181 fatalities, widespread building damage, liquefaction and landslides. The Christchurch earthquake was an aftershock of the M w 7.1 Darfield Earthquake of September 2010, occurring towards the eastern edge of the aftershock zone. This was a low recurrence earthquake for New Zealand and occurred on a fault unrecognised prior to the Darfield event. Geodetic and seismological source models show that oblique-reverse slip occurred along a northeastÁsouthwest-striking fault dipping southeast at c. 698, with maximum slip at 3Á4 km depth. Ground motions during the earthquake were unusually large at near-source distances for an earthquake of its size, registering up to 2.2 g (vertical) and 1.7 g (horizontal) near the epicentre and up to 0.8 g (vertical) and 0.7 g (horizontal) in the city centre. Acceleration response spectra exceeded 2500 yr building design codes and estimates based on standard New Zealand models. The earthquake was associated with high apparent stress indicative of a strong fault. Furthermore, rupture in an updip direction towards Christchurch likely led to strong directivity effects in the city. Site effects including long period amplification and near-surface effects also contributed to the severity of ground motions.

Changes in hot spring temperature and hydrogeology of the Alpine Fault hanging wall, New Zealand, induced by distal South Island earthquakes

“…The largest and most damaging aftershock was the Mw6.3 Christchurch earthquake at 12:51 (NZST) on 22 February 2011, which occurred on an oblique thrust fault beside the volcanic rocks of Banks Peninsula (Beavan et al 2011;Kaiser et al 2012) at a distance of 220 km from Copland hot spring.…”

Geophysical Imaging of Subsurface Earthquake-induced Liquefaction Features at Christchurch Boys High School, Christchurch, New Zealand

“…The most recent avulsion is represented by the Selwyn soils (Shulmeister et al, 1999), which have high liquefaction potential because of their average grain size, lack of compaction and high pore space (Cubrinovski et al, 2010). The surrounding Canterbury Plains are underlain by a series of normal faults that are mostly non-active, but some faults have been re-activated as strike-slip faults to accommodate excess strain (Dorn et al, 2010;Davey, 2011;Kaiser et al, 2012).…”

“…On February 22, 2011, a Mw 6.2 earthquake occurred beneath the city of Christchurch, New Zealand (Davey, 2011;Kaiser et al, 2012). Widespread damage, destruction and fatalities occurred, not the least of which was the widespread liquefaction that was experienced throughout the Christchurch area.…”

The tectonic and structural setting of the 4 September 2010 Darfield (Canterbury) earthquake sequence, New Zealand

“…The Port Hills seismic activity seems to be discretely separated and offset from the end of the Greendale Fault. The New Brighton 23 December 2011 aftershock sequence provides strong evidence for an offshore thrust striking southwest coming onshore to intersect the Port Hills fault (GeoNet 2011), of which the latter has accommodated a significant component of dextral strike-slip movement (Beavan et al 2011;Kaiser et al 2012). The thrust possibly extends under the south-dipping Port Hills fault footwall to intersect with the section activated by the 22 February 2011 M W 6.2 earthquake, triggered by an oblique thrust focal mechanism.…”

“…Large single-event offsets relative to surface rupture length on other Canterbury faults have been noted in the palaeoseismic record . A second anomaly is that thrust focal mechanisms are associated with both the M W 7.1 and M W 6.2 triggering events beginning each cycle of aftershocks dominated by strikeslip focal mechanisms (Gledhill et al 2011;Kaiser et al 2012). Of particular note is that the Charing Cross epicentre is c. 8 km north of the Greendale Fault rupture, and the offshore New Brighton M L 5.8 and 6.0 and related thrust aftershocks is up to 10 km north of the Port Hills on 23 December 2011 (GeoNet 2011).…”